Basic Promise example Imagine that, for some reason, you wanted to write a calculator that only works half of the time. In code, a “bad” calculator might look something like this: functionbadCalc(num1, num2){ returnnewPromise((resolve, reject)=>{ ...
times--;// 2. fetch 本身返回值就是 Promise,不需要再次使用 Promise 包裹returnfetch(url).then(value=>{if(value.status===200) {console.log(`✅ OK`, value);// 3. 手动返回 Promise 的 value, 没有返回值 默认返回 undefinedreturnvalue; }else{thrownewError(`❌ http code error:${value.st...
A promise in real life is just an assurance about ‘something’. So what happens when somebody makes a promise to you? They give you a guarantee based on which you can plan something. Now, the promise can either be kept or broken. So, when you keep a promise, you expect something out...
This is the tenth article in the series of exploring the principles of JS native methods. This article will introduce how to write a Promise A+ specification , and implement the Promise related methods by the way. Implement Promise/A+
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In JavaScript, promise.resolve is a method that creates a new Promise object that is resolved with a given value. This method is often used when working with
How to Create a JavaScript Promise We’re going to start by creating a promise which returns a user’s name. This function will return a user’s name to our program after three seconds. This will help us see how promises are used to write asynchronous code. To create a promise, we nee...
in newer Node.js APIs. You might have to write promise-based code in your work to wrap older APIs that won't be updated. By using promises for this wrapping, you allow the code to be used in a larger range of Node.js versioned projects than in the newer async/await style of code....
So while our previous examples will ensure we do the fewest API calls possible, we may want to tweak our solution to make an API call every so often as the user types. This would be a throttle function.How to write a throttle in JavaScript...
By Shimju David Posted June 2, 2017 In Javascript, ES6, ES7, React 0 0 Using Promises: A Promise in short: “Imagine you are a kid. Your mom promises you that she’ll get you a new phone next week.” That is a promise. A promise has 3 states. They are: 1. Promise is ...