This course has been updated! We now recommend you take the JavaScript Performance course.

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The "The Single Threaded Browser" Lesson is part of the full, Website Performance course featured in this preview video. Here's what you'd learn in this lesson:

Threading allows more than one operation at the same moment in time. Threaded programming can be very complex to implement. JavaScript, however is single threaded. Don’t confuse asynchronous programming with parallel programming. While JavaScript has asynchronous code execution, the event loop is single threaded. The UI Thread in the browser is single threaded. This means the CSS rendering engine, DOM, JavaScript engine, etc. are all on the same thread.

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