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For that, you simply define an argument as part of the callback. Mocha waits until the done func- tion is called. You can tweak this timeout by supplying the -t option to the mocha command. Because Mocha executes only one test at a time at any time, it knows to link any uncaught exceptions that are captured through pro- cess. In the following example, you test the behavior of Jade when supplied a template that contains a paragraph.
You use it in combination with expect. Each suite can have setup and teardown functions associated with them. These functions are executed prior to each test in the suite, and they avoid code repeti- tion while maximizing testing isolation. IO Part IV: Databases Chapter MongoDB Chapter MySQL Chapter Redis Part V: Testing Chapter Code Sharing Chapter This post offers clear idea in favor of the new viewers of blogging, that genuinely how to do blogging and site-building. You must be logged in to post a comment.
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Book Details. AMP is not what makes the biggest difference from a performance perspective. A benefit for the website owner is obvious: Obviously, a presence in a walled garden places developers in a position to produce and maintain a separate version of their content, and in case of Instant Articles and Apple News without actual URLs thanks Addy, Jeremy!
Notice that CDNs can serve and offload dynamic content as well. So, restricting your CDN to static assets is not necessary. Double-check whether your CDN performs compression and conversion e. Assets Optimizations Use Brotli or Zopfli for plain text compression. In , Google introduced Brotli , a new open-source lossless data format, which is now supported in all modern browsers.
In practice, Brotli appears to be much more effective than Gzip and Deflate. It might be very slow to compress, depending on the settings, but slower compression will ultimately lead to higher compression rates.
Still, it decompresses fast.
You can also estimate Brotli compression savings for your site. At the highest level of compression, Brotli is so slow that any potential gains in file size could be nullified by the amount of time it takes for the server to begin sending the response as it waits to dynamically compress the asset.
With static compression, however, higher compression settings are preferred. The catch is that files will take around 80 times longer to compress. The strategy? Make sure that the server handles content negotiation for Brotli or gzip properly. Other options are available , too. With JPEG, we can serve a "decent" user experience with the half or even quarter of the data and load the rest later, rather than have a half-empty image as it is in the case of WebP.
Your decision will depend on what you are after: On Smashing Magazine, we use the postfix -opt for image names — for example, brotli-compression-opt.
Every single image optimization article would state it, but keeping vector assets clean and tight is always worth reminding. Make sure to clean up unused assets, remove unnecessary metadata and reduces the amount of path points in artwork and thus SVG code.
Thanks, Jeremy! The future of responsive images might change dramatically with the adoption of client hints. Client hints are HTTP request header fields, e.
As a result, the server can decide how to fill in the layout with appropriately sized images, and serve only these images in desired formats.
With client hints, we move the resource selection from HTML markup and into the request-response negotiation between the client and server. Client hints provide annotations on resulting image requests that enable resource selection automation.
Service Worker provides full request and response management capabilities on the client. It holds true not only for image assets but for pretty much all other requests as well. Unfortunately, client hints still have to gain some browser support. Under consideration in Firefox. Not good enough? Well, you can also improve perceived performance for images with the multiple background images technique. Keep in mind that playing with contrast and blurring out unnecessary details or removing colors can reduce file size as well.
Ah, you need to enlarge a small photo without losing quality? Consider using Letsenhance. These optimizations so far cover just the basics. Addy Osmani has published a very detailed guide on Essential Image Optimization that goes very deep into details of image compression and color management.
For example, you could blur out unnecessary parts of the image by applying a Gaussian blur filter to them to reduce the file size, and eventually you might even start removing colors or turn the picture into black and white to reduce the size even further.
In the land of good news though, video formats have been advancing massively over the years. For a long time, we had hoped that WebM would become the format to rule them all, and WebP which is basically one still image inside of the WebM video container will become a replacement for dated image formats.
AV1 has compression similar to H. The H. AV1 just like H. For now, the most widely used and supported encoding is H. Boris Schapira provides exact instructions for FFmpeg to optimize videos to the maximum.
Of course, providing WebM format as an alternative would help, too.
Need a quick win? Zach Leatherman has a quick min tutorial and case study to get your fonts in order. Otherwise, font loading will cost you in the first render time. Still, it might be a good idea to be selective and choose files that matter most, e.
Nobody likes waiting for the content to be displayed. With the font-display CSS descriptor , we can control the font loading behavior and enable content to be readable immediately font-display: However, if you want to avoid text reflows , we still need to use the Font Loading API, specifically to group repaints , or when you are using third party hosts. Unless you can use Google Fonts with Cloudflare Workers , of course.
Talking about Google Fonts: Always self-host your fonts for maximum control if you can. In general, if you use font-display: Use preconnect for faster cross-origin font requests, but be cautious with preload as preloading fonts from a different origin will incur network contention. Also, it might be a good idea to opt out of web fonts or at least second stage render if the user has enabled Reduce Motion in accessibility preferences or has opted in for Data Saver Mode see Save-Data header.
To measure the web font loading performance, consider the All Text Visible metric the moment when all fonts have loaded and all content is displayed in web fonts , as well as Web Font Reflow Count after first render.
Obviously, the lower both metrics are, the better the performance is. They give designers a much broader design space for typographic choices, but it comes at the cost of a single serial request opposed to a number of individual file requests. That single request might be slow blocking the entire typographic appearance on the page.
Now, what would make a bulletproof web font loading strategy? Set up a spreadsheet. Define the basic core experience for legacy browsers i. When optimizing for performance we need to reflect our priorities. Load the core experience immediately, then enhancements , and then the extras. On its own, cutting-the-mustard deduces device capability from browser version, which is no longer something we can do today. For example, cheap Android phones in developing countries mostly run Chrome and will cut the mustard despite their limited memory and CPU capabilities.
When the Moon Split: A biography of Prophet Muhammad
Bottom line: Also, you might want to consider learning how to write efficient CSS selectors as well as how to avoid bloat and expensive styles. Feeling like going beyond that? You can also use Webpack to shorten the class names and use scope isolation to rename CSS class names dynamically at the compilation time. Code-splitting is another Webpack feature that splits your code base into "chunks" that are loaded on demand.
Front-End Performance Checklist 2019 [PDF, Apple Pages, MS Word]
Alexander Kondrov has a fantastic introduction to code-splitting with Webpack and React. Where to define split points? Umar Hansa explains how you can use Code Coverage from Devtools to achieve it. Typical use cases for web workers are prefetching data and Progressive Web Apps to load and store some data in advance so that you can use it later when needed. And you could use Comlink to streamline the communication between the main page and the worker.
Still some work to do, but we are getting there. Workerize allows you to move a module into a Web Worker, automatically reflecting exported functions as asynchronous proxies. Alternatively, you could use worker-plugin as well.
Shubham Kanodia has written a detailed low-maintenance guide on smart bundling: As a result, we help reduce blocking of the main thread by reducing the amount of scripts the browser needs to process.
First, set up metrics that tracks if the ratio of legacy code calls is staying constant or going down, not up.
You can use Puppeteer to programmatically collect code coverage and Canary already allows you to export code coverage results , too. As Andy Davies noted, you might want to collect code coverage for both modern and legacy browsers though. There are many other use-cases for Puppeteer , such as, for example, automatic visual diffing or monitoring unused CSS with every build.
After that, you set that specific image as a background on the corresponding selector in your CSS, sit back and wait for a few months if the file is going to appear in your logs. If there are no entries, nobody had that legacy component rendered on their screen:For tests in which exceptions could be raised in the future that is, as a result of asynchronous behavior , you want to tell Mocha that you will notify it when you consider the test complete.
Still, it decompresses fast. It combines great power and flexibility with a nice and clean syntax. You can simply disable compression to speed up Uglify builds by 3 to 4 times.
An Overview Chapter 3: Unfortunately, as Paul Lewis noticed , frameworks typically have no concept of priority that can be surfaced to developers, and hence progressive booting is difficult to implement with most libraries and frameworks. Be pessimistic in performance expectations, but be optimistic in interface design and use idle time wisely. It doesn't seem so.
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