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assignment Level : Intermediate
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Performance matters to users. Web developers need to build apps that react quickly and render smoothly. Google performance guru Paul Lewis is here to help you destroy jank and create web apps that maintain 60 frames per second performance. You'll leave this course with the tools you need to profile apps and identify the causes of jank. You'll explore the browser's rendering pipeline and uncover patterns that make it easy to build performant apps.

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*The News Aggregator App* - Turn an unusable app into a high performance, 60 frame per second experience. You'll be given a news aggregator app that uses the Hacker News API to display the day's top stories. The news aggregator has *lots* of performance issues. You'll demonstrate your understanding of performance by destroying all the jank and creating an experience that users will love.

Lesson 1 - The Critical Rendering Path

* You'll play Jank Invaders to develop your eye for jank! * You'll learn how the browser turns HTML into pixels on the page * You'll learn how different CSS styles affect the rendering pipeline differently.

Lesson 2 - App Lifecycles

* You'll learn how there are four distinct phases in an app's lifecycle: Response, Animation, Idle and Load (RAIL). * You'll learn how your frame budget changes depending on where the user is in RAIL. * You'll practice thinking through app workloads at different stages in RAIL.

Lesson 3 - Weapons of Jank Destruction

* You'll learn how to make sense of the Timeline panel in Chrome DevTools. * You'll practice profiling a few different apps to find the source of jank.

Lesson 4 - JavaScript

* You'll optimize JavaScript to hit 60fps during animations. * You'll move expensive JavaScript operations off the main thread and into Web Workers. * You'll debug a janky copy of a production quality app - the QR Snapper.

Lesson 5 - Styles and Layout

* You'll learn how accessing the wrong CSS properties at inopportune moments can create loads of extra work for the browser. * You'll debug multiple instances of one of the nastiest performance problems - Forced Synchronous Layout.

Lesson 6 - Compositing and Painting

* You'll practice profiling layer and paint performance with the paint profiler tool in the DevTools Timeline. * You'll manage and optimize layers to reduce the number of steps the browser needs to take to render each frame. * You'll demonstrate everything you've learned about performance as you de-jankify the News Aggregator App!


  • Paul Lewis - Paul works on the Google Chrome team as a Developer Advocate. He spends his days profiling runtime performance issues, and helping developers to build faster sites and apps. Do not be fooled by his extreme baldness; it's a solar panel for his cunning and guile.
  • Cameron Pittman - A passionate educator and programmer, Cameron lives and breathes web development as he creates programming courses at Udacity. Before coming here, Cameron was a combination Director of Content and web developer at Seattle startup LearnBIG. He taught four years of high school physics and chemistry in Nashville, TN, during which time he pioneered teaching physics with the video game Portal 2. Cameron graduated with a degree in physics and astronomy from Vanderbilt University and earned his master's in teaching from Belmont University.

Content Designer


Google is a company founded on 4 September 1998 in the Google garage in Silicon Valley, California, by Larry Page and Sergueï Brin, creators of the Google search engine.

The company made its name primarily through the monopolistic position of its search engine, which faced competition first from AltaVista and then from Yahoo! and Bing. It has since made a number of acquisitions and developments, and today owns a number of noteworthy software products and websites, including YouTube, the Android operating system for mobile phones, and other services such as Google Earth, Google Maps and Google Play.




Udacity is a for-profit educational organization founded by Sebastian Thrun, David Stavens, and Mike Sokolsky offering massive open online courses (MOOCs). According to Thrun, the origin of the name Udacity comes from the company's desire to be "audacious for you, the student". While it originally focused on offering university-style courses, it now focuses more on vocational courses for professionals.

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