av Principles of gravitational lensing: light deflection as a probe of astrophysics and cosmology / Arthur B. Congdon, Charles R. Keeton By library.mit.edu Published On :: Sun, 30 Dec 2018 13:10:00 EST Online Resource Full Article
av Probes of multimessenger astrophysics: charged cosmic rays, neutrinos, y-rays and gravitational waves / Maurizio Spurio By library.mit.edu Published On :: Sun, 20 Jan 2019 12:54:47 EST Online Resource Full Article
av International Symposium on Gravity, Geoid and Height Systems 2016: proceedings organized by IAG Commission 2 and the International Gravity Field Service, Thessaloniki, Greece, September 19-23, 2016 / editors, Georgios S. Vergos, Roland Pail and Riccardo B By library.mit.edu Published On :: Sun, 20 Jan 2019 12:54:47 EST Online Resource Full Article
av Extensions of f(R) gravity: curvature-matter couplings and hybrid metric-Palatini gravity / Tiberiu Harko (University College London), Francisco S.N. Lobo (Universidade de Lisboa) By library.mit.edu Published On :: Sun, 17 Feb 2019 13:12:16 EST Online Resource Full Article
av Stellar Populations and the Distance Scale: a conference in honor of Jeremy Mould: proceedings of a conference held at Kavli Institute for Astronomy and Astrophysics at Peking University, Beijing, China, 11-15 September 2017 / edited by Joseph B. Jensen, By library.mit.edu Published On :: Sun, 17 Feb 2019 13:12:16 EST Hayden Library - QB819.S74 2017 Full Article
av The physics and astrophysics of neutron stars Luciano Rezzolla, Pierre Pizzochero, David Ian Jones, Nanda Rea, Isaac Vidaña, editors By library.mit.edu Published On :: Sun, 17 Feb 2019 13:12:16 EST Online Resource Full Article
av Understanding the Enrichment of Heavy Elements by the Chemodynamical Evolution Models of Dwarf Galaxies / Hirai Yutaka By library.mit.edu Published On :: Sun, 19 May 2019 07:20:37 EDT Online Resource Full Article
av From Cave Man to Cave Martian: Living in Caves on the Earth, Moon and Mars / Manfred "Dutch" von Ehrenfried By library.mit.edu Published On :: Sun, 19 May 2019 07:20:37 EDT Online Resource Full Article
av Heavenly numbers: astronomy and authority in early imperial China / Christopher Cullen (Needham Research Institute and Darwin College, Cambridge, CRCAO, Paris, Sometime scholar of University College, Oxford, and Research Fellow of Clare Hall, Cambridge) By library.mit.edu Published On :: Sun, 26 May 2019 07:18:08 EDT Hayden Library - QB17.C853 2017 Full Article
av Advances in gravity and magnetic processing and interpretation / J. Derek Fairhead By library.mit.edu Published On :: Sun, 2 Jun 2019 07:11:36 EDT Online Resource Full Article
av Computational gas-solids flows and reacting systems: theory, methods and practice / [edited by] Sreekanth Pannala, Madhava Syamlal, Thomas J. O'Brien By library.mit.edu Published On :: Thu, 19 Dec 2013 15:20:36 EST Barker Library - TA357.5.M84 C646 2011 Full Article
av High accuracy computing methods: fluid flows and wave phenomena / Tapan K. Sengupta By library.mit.edu Published On :: Sun, 5 Jan 2014 06:05:41 EST Barker Library - TA357.5.D37 S46 2013 Full Article
av Numerical methods in contact mechanics / Vladislav A. Yastrebov By library.mit.edu Published On :: Sun, 1 Jun 2014 06:03:23 EDT Barker Library - TA353.Y37 2013 Full Article
av Advanced post-processing of experimental and numerical data: November 4-7, 2013 / edited by L. David & C. Schram By library.mit.edu Published On :: Sun, 31 May 2015 06:08:03 EDT Barker Library - TA357.5.D37 A38 2014 Full Article
av Fluid mechanics for engineers / David A. Chin, University of Miami By library.mit.edu Published On :: Sun, 23 Jul 2017 06:08:44 EDT Barker Library - TA357.C47384 2017 Full Article
av Vector mechanics for engineers. Ferdinand P. Beer,E. Russell Johnston, Jr., David F. Mazurek, Phillip J. Cornwell, Brian P. Self By library.mit.edu Published On :: Sun, 26 Nov 2017 06:08:41 EST Barker Library - TA350.V34 2016 Full Article
av A first course in vibrations and waves / Mohammad Samiullah By library.mit.edu Published On :: Sun, 10 Dec 2017 06:07:17 EST Barker Library - TA355.S36 2015 Full Article
av Statics and mechanics of materials / Ferdinand P. Beer, E. Russell Johnston, Jr., John T. DeWolf, David F. Mazurek By library.mit.edu Published On :: Sun, 22 Apr 2018 06:05:26 EDT Barker Library - TA351.S68 2017 Full Article
av Active flow control: techniques and applications / edited by S. Lavagnoli By library.mit.edu Published On :: Sun, 6 May 2018 06:05:21 EDT Barker Library - TA357.A28 2017 Full Article
av Generations / written & illustrated by Flavia Biondi By library.mit.edu Published On :: Sun, 13 May 2018 06:11:31 EDT Hayden Library - PN6767.B56 G46 2017 Full Article
av Saucer Country / written by Paul Cornell ; art by Ryan Kelly ; additional art by Jimmy Broxton, Goran Sudzuka, David Lapham, Mirko Colak, and Andrea Mutti ; colors by Giulia Brusco, Lee Loughridge, and Cris Peter ; letters by Sal Cipriano By library.mit.edu Published On :: Sun, 13 May 2018 06:11:31 EDT Hayden Library - PN6728.S28 C66 2017 Full Article
av Latinx superheroes in mainstream comics / Frederick Luis Aldama ; foreword by John Jennings ; afterword by Javier Hernandez By library.mit.edu Published On :: Sun, 12 Aug 2018 06:42:43 EDT Hayden Library - PN6725.A37 2017 Full Article
av The green hand and other stories / Nicole Claveloux ; with Edith Zha ; introduction by Daniel Clowes ; translated by Donald Nicholson-Smith ; English lettering by Dustin Harbin By library.mit.edu Published On :: Sun, 26 Aug 2018 06:43:45 EDT Hayden Library - PN6747.C53 A2 2017 Full Article
av The American way / John Ridley, writer ; Georges Jeanty, penciller ; Karl Story, Ray Snyder, inkers ; Wildstorm FX, colorist ; Pat Brosseau, Travis Lanham, Rob Leigh, letterers ; Georges Jeanty, Karl Story, Randy Mayor, series and collection cover artist By library.mit.edu Published On :: Sun, 30 Sep 2018 06:43:29 EDT Hayden Library - PN6728.A496 R53 2017 Full Article
av Las Meninas / Santiago García, Javier Olivares By library.mit.edu Published On :: Sun, 21 Oct 2018 06:39:51 EDT Hayden Library - PN6778.M46 G37 2016 Full Article
av Batgirl / Hope Larson, writer ; Rafael Albuquerque, artist ; Dave McCaig, colorist ; Deron Bennett, letterer ; Rafael Albuquerque, collection and original series cover artist By library.mit.edu Published On :: Sun, 28 Oct 2018 06:40:11 EDT Hayden Library - PN6728.B358 L37 2017 Full Article
av Black Panther: prelude / writer: Will Corona Pilgrim ; artist: Annapaola Martello ; colorist: Jordan Boyd ; letterer: VC's Travis Lanham ; editors: Mark Basso with Sarah Brunstad By library.mit.edu Published On :: Sun, 28 Oct 2018 06:40:11 EDT Hayden Library - PN6728.B53 P55 2017 Full Article
av Batwoman by Greg Rucka and J.H. Williams III / Greg Rucka, writer ; J.H. Williams III, Jock, Scott Kolins, artists ; Dave Stewart, David Baron, colorists ; Todd Klein, letterer ; J.H. Williams III, collection cover artist By library.mit.edu Published On :: Sun, 13 Jan 2019 09:27:20 EST Hayden Library - PN6728.B38 R82 2017 Full Article
av Ink in water: an illustrated memoir: or, How I kicked anorexia's ass and embraced body positivity! / Lacy J. Davis & Jim Kettner By library.mit.edu Published On :: Sun, 27 Jan 2019 09:25:35 EST Hayden Library - PN6727.D375 I55 2017 Full Article
av River runners : a tale of hardship and bravery / by James Houston ; drawings by the author By darius.uleth.ca Published On :: Toronto : Mclelland and Stewart Limited, 1979 Full Article
av New on the Web: Rare Muslim American Slave Narrative Now Online By www.loc.gov Published On :: Tue, 15 Jan 2019 13:29:50 -0600 The Library of Congress has acquired and made available online the Omar Ibn Said Collection, which includes the only known surviving slave narrative written in Arabic in the United States. In 1831, Omar Ibn Said, a wealthy and highly educated man who was captured in West Africa and brought to the United States as a slave, wrote a 15-page autobiography describing his experiences. Read more about the extraordinary Omar Ibn Said Collection. Full Article
av Scientific ontology : integrating naturalized metaphysics and voluntarist epistemology / by Anjan Chakravartty. By darius.uleth.ca Published On :: Oxford, UK ; New York, NY : Oxford University Press, [2017] Full Article
av Water and wastewater engineering: design principles and practice / Mackenzie L. Davis By library.mit.edu Published On :: Sun, 23 Feb 2020 06:28:52 EST Barker Library - TD345.D36 2020 Full Article
av The five-ton life: carbon, America, and the culture that may save us / Susan Subak By library.mit.edu Published On :: Sun, 26 Apr 2020 06:32:35 EDT Dewey Library - TD885.5.C3 S83 2018 Full Article
av Red, green, and blue: the partisan divide on environmental issues / David Karol By library.mit.edu Published On :: Sun, 26 Apr 2020 06:32:35 EDT Dewey Library - GE197.K37 2019 Full Article
av Disordered wax platelets on Tradescantia pallida leaves create golden shine By feeds.rsc.org Published On :: Faraday Discuss., 2020, Accepted ManuscriptDOI: 10.1039/D0FD00024H, PaperGea Theodora van de Kerkhof, Lukas Schertel, Rebecca Poon, Gianni Jacucci, Beverley Jane Glover, Silvia VignoliniPlants have various strategies to protect themselves from harmful light...The content of this RSS Feed (c) The Royal Society of Chemistry Full Article
av Cultural differences and the practice of sexual medicine: a guide for sexual health practitioners / David L. Rowland, Emmanuele A. Jannini, editors By library.mit.edu Published On :: Sun, 15 Mar 2020 06:46:24 EDT Online Resource Full Article
av Transforming global health: interdisciplinary challenges, perspectives, and strategies / Korydon H. Smith, Pavani Kalluri Ram, editors By library.mit.edu Published On :: Sun, 15 Mar 2020 06:46:24 EDT Online Resource Full Article
av Regulatory stewardship of health research: navigating participant protection and research promotion / Edward S. Dove (School of Law, The University of Edinburgh, UK) By library.mit.edu Published On :: Sun, 22 Mar 2020 06:38:46 EDT Online Resource Full Article
av Opioid therapy in infants, children, and adolescents Ravi D. Shah, Santhanam Suresh, editors By library.mit.edu Published On :: Sun, 5 Apr 2020 06:39:21 EDT Online Resource Full Article
av Perioperative care of the orthopedic patient / C. Ronald MacKenzie, Charles N. Cornell, Stavros G. Memtsoudis, editors By library.mit.edu Published On :: Sun, 26 Apr 2020 07:06:33 EDT Online Resource Full Article
av Local wound care for dermatologists / Afsaneh Alavi, Howard I. Maibach, editors By library.mit.edu Published On :: Sun, 26 Apr 2020 07:06:33 EDT Online Resource Full Article
av Havana syndrome: mass psychogenic illness and the real story behind the embassy mystery and hysteria / Robert W. Baloh, Robert E. Bartholomew By library.mit.edu Published On :: Sun, 26 Apr 2020 07:06:33 EDT Online Resource Full Article
av Heaviest element could have fascinating atomic and nuclear spectra By feedproxy.google.com Published On :: 2018-02-12T09:27:39Z Simulations suggest oganesson has extremely smooth electron and nucleon distributions Full Article
av Physicists beat Lorentz reciprocity for microwave transmission By feedproxy.google.com Published On :: 2018-02-22T14:27:47Z New device could boost telecommunications and be adapted for photonics Full Article
av 25 Useful Resources for Creating Tooltips With JavaScript or CSS By designshack.net Published On :: Fri, 23 Aug 2013 01:00:50 +0000 Tooltips are awesome, there’s simply no denying it. They provide a simple, predictable and straightforward way to provide your users with useful, context-sensitive information, and they look cool to boot. We all agree on how great tooltips are, but how we go about implementing them can differ dramatically. If you’re at square one, looking for […] Full Article JavaScript CSS tooltip
av Code a Single-Page Sliding Website Layout With Fixed Navigation By designshack.net Published On :: Wed, 04 Sep 2013 14:00:28 +0000 When constructing a simple webpage, it can often make sense to fit the content into a single layout rather than multiple pages. These single-page websites are beneficial when you have a small project or portfolio which needs some online presence. If you split up content into neat sections, then visitors might use a small sliding […] Full Article JavaScript Navigation navigtion singlepage sliding
av Tab Discarding in Chrome: a Memory-Saving Experiment By feedproxy.google.com Published On :: Tue, 01 Sep 2015 00:00:00 +0000 Full Article
av Responsible JavaScript: Part I By feedproxy.google.com Published On :: 2019-03-28T09:07:40+00:00 By the numbers, JavaScript is a performance liability. If the trend persists, the median page will be shipping at least 400 KB of it before too long, and that’s merely what’s transferred. Like other text-based resources, JavaScript is almost always served compressed—but that might be the only thing we’re getting consistently right in its delivery. Unfortunately, while reducing resource transfer time is a big part of that whole performance thing, compression has no effect on how long browsers take to process a script once it arrives in its entirety. If a server sends 400 KB of compressed JavaScript, the actual amount browsers have to process after decompression is north of a megabyte. How well devices cope with these heavy workloads depends, well, on the device. Much has been written about how adept various devices are at processing lots of JavaScript, but the truth is, the amount of time it takes to process even a trivial amount of it varies greatly between devices. Take, for example, this throwaway project of mine, which serves around 23 KB of uncompressed JavaScript. On a mid-2017 MacBook Pro, Chrome chews through this comparably tiny payload in about 25 ms. On a Nokia 2 Android phone, however, that figure balloons to around 190 ms. That’s not an insignificant amount of time, but in either case, the page gets interactive reasonably fast. Now for the big question: how do you think that little Nokia 2 does on an average page? It chokes. Even on a fast connection, browsing the web on it is an exercise in patience as JavaScript-laden web pages brick it for considerable stretches of time. Figure 1. A performance timeline overview of a Nokia 2 Android phone browsing on a page where excessive JavaScript monopolizes the main thread. While devices and the networks they navigate the web on are largely improving, we’re eating those gains as trends suggest. We need to use JavaScript responsibly. That begins with understanding what we’re building as well as how we’re building it. The mindset of “sites” versus “apps” Nomenclature can be strange in that we sometimes loosely identify things with terms that are inaccurate, yet their meanings are implicitly understood by everyone. Sometimes we overload the term “bee” to also mean “wasp”, even though the differences between bees and wasps are substantial. Those differences can motivate you to deal with each one differently. For instance, we’ll want to destroy a wasp nest, but because bees are highly beneficial and vulnerable insects, we may opt to relocate them. We can be just as fast and loose in interchanging the terms “website” and “web app”. The differences between them are less clear than those between yellowjackets and honeybees, but conflating them can bring about painful outcomes. The pain comes in the affordances we allow ourselves when something is merely a “website” versus a fully-featured “web app.” If you’re making an informational website for a business, you’re less likely to lean on a powerful framework to manage changes in the DOM or implement client-side routing—at least, I hope. Using tools so ill-suited for the task would not only be a detriment to the people who use that site but arguably less productive. When we build a web app, though, look out. We’re installing packages which usher in hundreds—if not thousands—of dependencies, some of which we’re not sure are even safe. We’re also writing complicated configurations for module bundlers. In this frenzied, yet ubiquitous, sort of dev environment, it takes knowledge and vigilance to ensure what gets built is fast and accessible. If you doubt this, run npm ls --prod in your project’s root directory and see if you recognize everything in that list. Even if you do, that doesn’t account for third party scripts—of which I’m sure your site has at least a few. What we tend to forget is that the environment websites and web apps occupy is one and the same. Both are subject to the same environmental pressures that the large gradient of networks and devices impose. Those constraints don’t suddenly vanish when we decide to call what we build “apps”, nor do our users’ phones gain magical new powers when we do so. It’s our responsibility to evaluate who uses what we make, and accept that the conditions under which they access the internet can be different than what we’ve assumed. We need to know the purpose we’re trying to serve, and only then can we build something that admirably serves that purpose—even if it isn’t exciting to build. That means reassessing our reliance on JavaScript and how the use of it—particularly to the exclusion of HTML and CSS—can tempt us to adopt unsustainable patterns which harm performance and accessibility. Don’t let frameworks force you into unsustainable patterns I’ve been witness to some strange discoveries in codebases when working with teams that depend on frameworks to help them be highly productive. One characteristic common among many of them is that poor accessibility and performance patterns often result. Take the React component below, for example: import React, { Component } from "react"; import { validateEmail } from "helpers/validation"; class SignupForm extends Component { constructor (props) { super(props); this.handleSubmit = this.handleSubmit.bind(this); this.updateEmail = this.updateEmail.bind(this); this.state.email = ""; } updateEmail (event) { this.setState({ email: event.target.value }); } handleSubmit () { // If the email checks out, submit if (validateEmail(this.state.email)) { // ... } } render () { return ( Enter your email: Sign Up ); } } There are some notable accessibility issues here: A form that doesn’t use a <form> element is not a form. Indeed, you could paper over this by specifying role="form" in the parent <div>, but if you’re building a form—and this sure looks like one—use a <form> element with the proper action and method attributes. The action attribute is crucial, as it ensures the form will still do something in the absence of JavaScript—provided the component is server-rendered, of course.A <span> is not a substitute for a <label> element, which provides accessibility benefits <span>s don’t.If we intend to do something on the client side prior to submitting a form, then we should move the action bound to the <button> element's onClick handler to the <form> element’s onSubmit handler.Incidentally, why use JavaScript to validate an email address when HTML5 offers form validation controls in almost every browser back to IE 10? There’s an opportunity here to rely on the browser and use an appropriate input type, as well as the required attribute—but be aware that getting this to work right with screen readers takes a little know-how.While not an accessibility issue, this component doesn't rely on any state or lifecycle methods, which means it can be refactored into a stateless functional component, which uses considerably less JavaScript than a full-fledged React component. Knowing these things, we can refactor this component: import React from "react"; const SignupForm = props => { const handleSubmit = event => { // Needed in case we're sending data to the server XHR-style // (but will still work if server-rendered with JS disabled). event.preventDefault(); // Carry on... }; return ( <form method="POST" action="/signup" onSubmit={handleSubmit}> <label for="email" class="email-label">Enter your email:</label> <input type="email" id="email" required /> <button>Sign Up</button> </form> ); }; Not only is this component now more accessible, but it also uses less JavaScript. In a world that’s drowning in JavaScript, deleting lines of it should feel downright therapeutic. The browser gives us so much for free, and we should try to take advantage of that as often as possible. This is not to say that inaccessible patterns occur only when frameworks are used, but rather that a sole preference for JavaScript will eventually surface gaps in our understanding of HTML and CSS. These knowledge gaps will often result in mistakes we may not even be aware of. Frameworks can be useful tools that increase our productivity, but continuing education in core web technologies is essential to creating usable experiences, no matter what tools we choose to use. Rely on the web platform and you’ll go far, fast While we’re on the subject of frameworks, it must be said that the web platform is a formidable framework of its own. As the previous section showed, we’re better off when we can rely on established markup patterns and browser features. The alternative is to reinvent them, and invite all the pain such endeavors all but guarantee us, or worse: merely assume that the author of every JavaScript package we install has solved the problem comprehensively and thoughtfully. SINGLE PAGE APPLICATIONS One of the tradeoffs developers are quick to make is to adopt the single page application (SPA) model, even if it’s not a fit for the project. Yes, you do gain better perceived performance with the client-side routing of an SPA, but what do you lose? The browser’s own navigation functionality—albeit synchronous—provides a slew of benefits. For one, history is managed according to a complex specification. Users without JavaScript—be it by their own choice or not—won’t lose access altogether. For SPAs to remain available when JavaScript is not, server-side rendering suddenly becomes a thing you have to consider. Figure 2. A comparison of an example app loading on a slow connection. The app on the left depends entirely upon JavaScript to render a page. The app on the right renders a response on the server, but then uses client-side hydration to attach components to the existing server-rendered markup. Accessibility is also harmed if a client-side router fails to let people know what content on the page has changed. This can leave those reliant on assistive technology to suss out what changes have occurred on the page, which can be an arduous task. Then there’s our old nemesis: overhead. Some client-side routers are very small, but when you start with React, a compatible router, and possibly even a state management library, you’re accepting that there’s a certain amount of code you can never optimize away—approximately 135 KB in this case. Carefully consider what you’re building and whether a client side router is worth the tradeoffs you’ll inevitably make. Typically, you’re better off without one. If you’re concerned about the perceived navigation performance, you could lean on rel=prefetch to speculatively fetch documents on the same origin. This has a dramatic effect on improving perceived loading performance of pages, as the document is immediately available in the cache. Because prefetches are done at a low priority, they’re also less likely to contend with critical resources for bandwidth. Figure 3. The HTML for the writing/ URL is prefetched on the initial page. When the writing/ URL is requested by the user, the HTML for it is loaded instantaneously from the browser cache. The primary drawback with link prefetching is that you need to be aware that it can be potentially wasteful. Quicklink, a tiny link prefetching script from Google, mitigates this somewhat by checking if the current client is on a slow connection—or has data saver mode enabled—and avoids prefetching links on cross-origins by default. Service workers are also hugely beneficial to perceived performance for returning users, whether we use client side routing or not—provided you know the ropes. When we precache routes with a service worker, we get many of the same benefits as link prefetching, but with a much greater degree of control over requests and responses. Whether you think of your site as an “app” or not, adding a service worker to it is perhaps one of the most responsible uses of JavaScript that exists today. JAVASCRIPT ISN’T THE SOLUTION TO YOUR LAYOUT WOES If we’re installing a package to solve a layout problem, proceed with caution and ask “what am I trying to accomplish?” CSS is designed to do this job, and requires no abstractions to use effectively. Most layout issues JavaScript packages attempt to solve, like box placement, alignment, and sizing, managing text overflow, and even entire layout systems, are solvable with CSS today. Modern layout engines like Flexbox and Grid are supported well enough that we shouldn’t need to start a project with any layout framework. CSS is the framework. When we have feature queries, progressively enhancing layouts to adopt new layout engines is suddenly not so hard. /* Your mobile-first, non-CSS grid styles goes here */ /* The @supports rule below is ignored by browsers that don't support CSS grid, _or_ don't support @supports. */ @supports (display: grid) { /* Larger screen layout */ @media (min-width: 40em) { /* Your progressively enhanced grid layout styles go here */ } } Using JavaScript solutions for layout and presentations problems is not new. It was something we did when we lied to ourselves in 2009 that every website had to look in IE6 exactly as it did in the more capable browsers of that time. If we’re still developing websites to look the same in every browser in 2019, we should reassess our development goals. There will always be some browser we’ll have to support that can’t do everything those modern, evergreen browsers can. Total visual parity on all platforms is not only a pursuit made in vain, it’s the principal foe of progressive enhancement. I’m not here to kill JavaScript Make no mistake, I have no ill will toward JavaScript. It’s given me a career and—if I’m being honest with myself—a source of enjoyment for over a decade. Like any long-term relationship, I learn more about it the more time I spend with it. It’s a mature, feature-rich language that only gets more capable and elegant with every passing year. Yet, there are times when I feel like JavaScript and I are at odds. I am critical of JavaScript. Or maybe more accurately, I’m critical of how we’ve developed a tendency to view it as a first resort to building for the web. As I pick apart yet another bundle not unlike a tangled ball of Christmas tree lights, it’s become clear that the web is drunk on JavaScript. We reach for it for almost everything, even when the occasion doesn’t call for it. Sometimes I wonder how vicious the hangover will be. In a series of articles to follow, I’ll be giving more practical advice to follow to stem the encroaching tide of excessive JavaScript and how we can wrangle it so that what we build for the web is usable—or at least more so—for everyone everywhere. Some of the advice will be preventative. Some will be mitigating “hair of the dog” measures. In either case, the outcomes will hopefully be the same. I believe that we all love the web and want to do right by it, but I want us to think about how to make it more resilient and inclusive for all. Full Article
av Responsible JavaScript: Part II By feedproxy.google.com Published On :: 2019-06-13T13:30:28+00:00 You and the rest of the dev team lobbied enthusiastically for a total re-architecture of the company’s aging website. Your pleas were heard by management—even up to the C-suite—who gave the green light. Elated, you and the team started working with the design, copy, and IA teams. Before long, you were banging out new code. It started out innocently enough with an npm install here and an npm install there. Before you knew it, though, you were installing production dependencies like an undergrad doing keg stands without a care for the morning after. Then you launched. Unlike the aftermath of most copious boozings, the agony didn’t start the morning after. Oh, no. It came months later in the ghastly form of low-grade nausea and headache of product owners and middle management wondering why conversions and revenue were both down since the launch. It then hit a fever pitch when the CTO came back from a weekend at the cabin and wondered why the site loaded so slowly on their phone—if it indeed ever loaded at all. Everyone was happy. Now no one is happy. Welcome to your first JavaScript hangover. It’s not your fault When you’re grappling with a vicious hangover, “I told you so” would be a well-deserved, if fight-provoking, rebuke—assuming you could even fight in so sorry a state. When it comes to JavaScript hangovers, there’s plenty of blame to dole out. Pointing fingers is a waste of time, though. The landscape of the web today demands that we iterate faster than our competitors. This kind of pressure means we’re likely to take advantage of any means available to be as productive as possible. That means we’re more likely—but not necessarily doomed—to build apps with more overhead, and possibly use patterns that can hurt performance and accessibility. Web development isn't easy. It’s a long slog we rarely get right on the first try. The best part of working on the web, however, is that we don’t have to get it perfect at the start. We can make improvements after the fact, and that’s just what the second installment of this series is here for. Perfection is a long ways off. For now, let’s take the edge off of that JavaScript hangover by improving your site’s, er, scriptuation in the short term. Round up the usual suspects It might seem rote, but it’s worth going through the list of basic optimizations. It’s not uncommon for large development teams—particularly those that work across many repositories or don’t use optimized boilerplate—to overlook them. Shake those trees First, make sure your toolchain is configured to perform tree shaking. If tree shaking is new to you, I wrote a guide on it last year you can consult. The short of it is that tree shaking is a process in which unused exports in your codebase don’t get packaged up in your production bundles. Tree shaking is available out of the box with modern bundlers such as webpack, Rollup, or Parcel. Grunt or gulp—which are not bundlers, but rather task runners—won’t do this for you. A task runner doesn’t build a dependency graph like a bundler does. Rather, they perform discrete tasks on the files you feed to them with any number of plugins. Task runners can be extended with plugins to use bundlers to process JavaScript. If extending task runners in this way is problematic for you, you’ll likely need to manually audit and remove unused code. For tree shaking to be effective, the following must be true: Your app logic and the packages you install in your project must be authored as ES6 modules. Tree shaking CommonJS modules isn’t practically possible.Your bundler must not transform ES6 modules into another module format at build time. If this happens in a toolchain that uses Babel, @babel/preset-env configuration must specify modules: false to prevent ES6 code from being converted to CommonJS. On the off chance tree shaking isn’t occurring during your build, getting it to work may help. Of course, its effectiveness varies on a case-by-case basis. It also depends on whether the modules you import introduce side effects, which may influence a bundler’s ability to shake unused exports. Split that code Chances are good that you’re employing some form of code splitting, but it’s worth re-evaluating how you’re doing it. No matter how you’re splitting code, there are two questions that are always worth asking yourself: Are you deduplicating common code between entry points?Are you lazy loading all the functionality you reasonably can with dynamic import()? These are important because reducing redundant code is essential to performance. Lazy loading functionality also improves performance by lowering the initial JavaScript footprint on a given page. On the redundancy front, using an analysis tool such as Bundle Buddy can help you find out if you have a problem. Bundle Buddy can examine your webpack compilation statistics and determine how much code is shared between your bundles. Where lazy loading is concerned, it can be a bit difficult to know where to start looking for opportunities. When I look for opportunities in existing projects, I’ll search for user interaction points throughout the codebase, such as click and keyboard events, and similar candidates. Any code that requires a user interaction to run is a potentially good candidate for dynamic import(). Of course, loading scripts on demand brings the possibility that interactivity could be noticeably delayed, as the script necessary for the interaction must be downloaded first. If data usage is not a concern, consider using the rel=prefetch resource hint to load such scripts at a low priority that won’t contend for bandwidth against critical resources. Support for rel=prefetch is good, but nothing will break if it’s unsupported, as such browsers will ignore markup they doesn’t understand. Externalize third-party hosted code Ideally, you should self-host as many of your site’s dependencies as possible. If for some reason you must load dependencies from a third party, mark them as externals in your bundler’s configuration. Failing to do so could mean your website’s visitors will download both locally hosted code and the same code from a third party. Let’s look at a hypothetical situation where this could hurt you: say that your site loads Lodash from a public CDN. You've also installed Lodash in your project for local development. However, if you fail to mark Lodash as external, your production code will end up loading a third party copy of it in addition to the bundled, locally hosted copy. This may seem like common knowledge if you know your way around bundlers, but I’ve seen it get overlooked. It’s worth your time to check twice. If you aren’t convinced to self-host your third-party dependencies, then consider adding dns-prefetch, preconnect, or possibly even preload hints for them. Doing so can lower your site’s Time to Interactive and—if JavaScript is critical to rendering content—your site’s Speed Index. Smaller alternatives for less overhead Userland JavaScript is like an obscenely massive candy store, and we as developers are awed by the sheer amount of open source offerings. Frameworks and libraries allow us to extend our applications to quickly do all sorts of stuff that would otherwise take loads of time and effort. While I personally prefer to aggressively minimize the use of client-side frameworks and libraries in my projects, their value is compelling. Yet, we do have a responsibility to be a bit hawkish when it comes to what we install. When we’ve already built and shipped something that depends on a slew of installed code to run, we’ve accepted a baseline cost that only the maintainers of that code can practically address. Right? Maybe, but then again, maybe not. It depends on the dependencies used. For instance, React is extremely popular, but Preact is an ultra-small alternative that largely shares the same API and retains compatibility with many React add-ons. Luxon and date-fns are much more compact alternatives to moment.js, which is not exactly tiny. Libraries such as Lodash offer many useful methods. Yet, some of them are easily replaceable with native ES6. Lodash’s compact method, for example, is replaceable with the filter array method. Many more can be replaced without much effort, and without the need for pulling in a large utility library. Whatever your preferred tools are, the idea is the same: do some research to see if there are smaller alternatives, or if native language features can do the trick. You may be surprised at how little effort it may take you to seriously reduce your app’s overhead. Differentially serve your scripts There’s a good chance you’re using Babel in your toolchain to transform your ES6 source into code that can run on older browsers. Does this mean we’re doomed to serve giant bundles even to browsers that don’t need them, until the older browsers disappear altogether? Of course not! Differential serving helps us get around this by generating two different builds of your ES6 source: Bundle one, which contains all the transforms and polyfills required for your site to work on older browsers. You’re probably already serving this bundle right now.Bundle two, which contains little to none of the transforms and polyfills because it targets modern browsers. This is the bundle you’re probably not serving—at least not yet. Achieving this is a bit involved. I’ve written a guide on one way you can do it, so there’s no need for a deep dive here. The long and short of it is that you can modify your build configuration to generate an additional but smaller version of your site’s JavaScript code, and serve it only to modern browsers. The best part is that these are savings you can achieve without sacrificing any features or functionality you already offer. Depending on your application code, the savings could be quite significant. A webpack-bundle-analyzer analysis of a project's legacy bundle (left) versus one for a modern bundle (right). View full-sized image. The simplest pattern for serving these bundles to their respective platforms is brief. It also works a treat in modern browsers: <!-- Modern browsers load this file: --> <script type="module" src="/js/app.mjs"></script> <!-- Legacy browsers load this file: --> <script defer nomodule src="/js/app.js"></script> Unfortunately, there’s a caveat with this pattern: legacy browsers like IE 11—and even relatively modern ones such as Edge versions 15 through 18—will download both bundles. If this is an acceptable trade-off for you, then worry no further. On the other hand, you'll need a workaround if you’re concerned about the performance implications of older browsers downloading both sets of bundles. Here’s one potential solution that uses script injection (instead of the script tags above) to avoid double downloads on affected browsers: var scriptEl = document.createElement("script"); if ("noModule" in scriptEl) { // Set up modern script scriptEl.src = "/js/app.mjs"; scriptEl.type = "module"; } else { // Set up legacy script scriptEl.src = "/js/app.js"; scriptEl.defer = true; // type="module" defers by default, so set it here. } // Inject! document.body.appendChild(scriptEl); This script infers that if a browser supports the nomodule attribute in the script element, it understands type="module". This ensures that legacy browsers only get legacy scripts and modern browsers only get modern ones. Be warned, though, that dynamically injected scripts load asynchronously by default, so set the async attribute to false if dependency order is crucial. Transpile less I’m not here to trash Babel. It’s indispensable, but lordy, it adds a lot of extra stuff without your ever knowing. It pays to peek under the hood to see what it’s up to. Some minor changes in your coding habits can have a positive impact on what Babel spits out. https://twitter.com/_developit/status/1110229993999777793 To wit: default parameters are a very handy ES6 feature you probably already use: function logger(message, level = "log") { console[level](message); } The thing to pay attention to here is the level parameter, which has a default of “log.” This means if we want to invoke console.log with this wrapper function, we don’t need to specify level. Great, right? Except when Babel transforms this function, the output looks like this: function logger(message) { var level = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : "log"; console[level](message); } This is an example of how, despite our best intentions, developer conveniences can backfire. What was a handful of bytes in our source has now been transformed into much larger in our production code. Uglification can’t do much about it either, as arguments can’t be reduced. Oh, and if you think rest parameters might be a worthy antidote, Babel’s transforms for them are even bulkier: // Source function logger(...args) { const [level, message] = args; console[level](message); } // Babel output function logger() { for (var _len = arguments.length, args = new Array(_len), _key = 0; _key < _len; _key++) { args[_key] = arguments[_key]; } const level = args[0], message = args[1]; console[level](message); } Worse yet, Babel transforms this code even for projects with a @babel/preset-env configuration targeting modern browsers, meaning the modern bundles in your differentially served JavaScript will be affected too! You could use loose transforms to soften the blow—and that’s a fine idea, as they’re often quite a bit smaller than their more spec-compliant counterparts—but enabling loose transforms can cause issues if you remove Babel from your build pipeline later on. Regardless of whether you decide to enable loose transforms, here’s one way to cut the cruft of transpiled default parameters: // Babel won't touch this function logger(message, level) { console[level || "log"](message); } Of course, default parameters aren’t the only feature to be wary of. For example, spread syntax gets transformed, as do arrow functions and a whole host of other stuff. If you don’t want to avoid these features altogether, you have a couple ways of reducing their impact: If you’re authoring a library, consider using @babel/runtime in concert with @babel/plugin-transform-runtime to deduplicate the helper functions Babel puts into your code.For polyfilled features in apps, you can include them selectively with @babel/polyfill via @babel/preset-env’s useBuiltIns: "usage" option. This is solely my opinion, but I believe the best choice is to avoid transpilation altogether in bundles generated for modern browsers. That’s not always possible, especially if you use JSX, which must be transformed for all browsers, or if you’re using bleeding edge language features that aren’t widely supported. In the latter case, it might be worth asking if those features are really necessary to deliver a good user experience (they rarely are). If you arrive at the conclusion that Babel must be a part of your toolchain, then it’s worth peeking under the hood from time to time to catch suboptimal stuff Babel might be doing that you can improve on. Improvement is not a race As you massage your temples wondering when this horrid JavaScript hangover is going to lift, understand that it’s precisely when we rush to get something out there as fast as we possibly can that the user experience can suffer. As the web development community obsesses on iterating faster in the name of competition, it’s worth your time to slow down a little bit. You’ll find that by doing so, you may not be iterating as fast as your competitors, but your product will be faster than theirs. As you take these suggestions and apply them to your codebase, know that progress doesn’t spontaneously happen overnight. Web development is a job. The truly impactful work is done when we’re thoughtful and dedicated to the craft for the long haul. Focus on steady improvements. Measure, test, repeat, and your site’s user experience will improve, and you’ll get faster bit by bit over time. Special thanks to Jason Miller for tech editing this piece. Jason is the creator and one of the many maintainers of Preact, a vastly smaller alternative to React with the same API. If you use Preact, please consider supporting Preact through Open Collective. Full Article