Some of those courses are also distributed on other platforms, like Pluralsight, Lynda. Uploaded by narabot on January 30, Internet Archive's 25th Anniversary Logo. Search icon An illustration of a magnifying glass. User icon An illustration of a person's head and chest. Sign up Log in. Web icon An illustration of a computer application window Wayback Machine Texts icon An illustration of an open book. Books Video icon An illustration of two cells of a film strip. Video Audio icon An illustration of an audio speaker.
YDKJS on twitter. This is a series of books diving deep into the core mechanisms of the JavaScript language. This is the second edition of the book series:. To read more about the motivations and perspective behind this book series, check out the Preface. If you're looking for the previous first edition books, they can be found here. Frontend Masters is the gold standard for top-of-the-line expert training material in frontend-oriented software development.
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I want to extend a warm and deep thanks to Marc Grabanski and the entire Frontend Masters team, not only for their excellent work with the video training platform, but for their unwavering support of me and of the "You Don't Know JS" books!
This edition of the books is being self-published through GetiPub publishing. The published books will be made available for sale through normal book retail sources. This was just a brief overview of Promise theory and behavior. Promises are genuine instances of the Promise.. However, there are promise-like objects called thenables that generally can interoperate with the Promise mechanisms.
Any object or function with a then.. Any place where the Promise mechanisms can accept and adopt the state of a genuine promise, they can also handle a thenable. Thenables are basically a general label for any promise-like value that may have been created by some other system than the actual Promise.. In that perspective, a thenable is generally less trustable than a genuine Promise.
Consider this misbehaving thenable, for example:. If you received that thenable and chained it with th. Prior to ES6, there was never any special reservation made on methods called then.. The most likely case of mistaken thenable will be async libraries that use then.. The onus will be on you to guard against directly using values with the Promise mechanism that would be incorrectly assumed to be a thenable.
The same goes for resolving with a promise:. Any value that you are not already certain is a trustable promise—even if it could be an immediate value—can be normalized by passing it to Promise. While resolve.. It returns a promise back that will be fulfilled if all the values fulfill, or reject immediately once the first of any of them rejects. While Promise. This is a strange inconsistency, and speaks to the suggestion that you should never use these methods with empty arrays.
No matter how much experience you have with JavaScript, odds are you don t fully understand the language. Armed with this knowledge, you can achieve true JavaScript mastery.
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