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Rediscovering JavaScript by Venkat Subramaniam

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Ways to Create a Promise

In order to return a promise, asynchronous functions have to first create a promise. If the asynchronous function finds that the task at hand is time consuming, it will internally hold a reference to the promise it creates and return the promise instantaneously to its caller. Once the task is completed, it will pass the result or the error through that promise. However, if the asynchronous function can quickly complete the task at hand, then it can return the promise in the resolved state instead of the pending state, making the result available to the caller right away through the promise. Likewise, if the asynchronous function finds an error in the input parameters given to it, or decides to return an error for any ...

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