Detailed explanation of Promise and Async in JS

Because Javascript is a single-threaded language, synchronous code executes only one line at a time. This means that if the synchronous code runs for more than an instant, it will stop the rest of the code from running until it finishes running. To prevent code with an indeterminate runtime from blocking other code from running, we need to use asynchronous code. Promise For this, we can use Promise in our code. A Promise represents an object whose process runs for an indeterminate time and may result in success or failure. To create a promise in Javascript, we use the constructor of the Promise object to create the promise. The Promise constructor accepts a fulfillment function with resolve and reject parameters. Both parameters are also functions, which allow us to call back the promise fulfillment (successful call gets a return value) or rejection (returns an error value and marks the promise as failed). The return value of the function is ignored. Therefore, promises can only return promises. For example, we define a promise in Javascript like the following code: const promise = new Promise((resolve, reject) = > { setTimeout(() => resolve('abc'), 1000); }); The code above creates a promise that returns…