自制ES6 Promise

最新推荐文章于 2024-04-29 04:13:10 发布

diandian82

最新推荐文章于 2024-04-29 04:13:10 发布

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分类专栏： Javascript Node.JS 文章标签： Javascript Promise C

本文链接：https://blog.youkuaiyun.com/diandian82/article/details/78877910

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本文介绍了一个简单的Promise实现方法，包括基本构造和链式调用功能，并通过具体示例展示了如何使用该自定义Promise进行异步操作。

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Checked all Promise sample, none of them is in ES6 syntax, this is weird, which age are we now. Simplest verison

class MyPromise {
    constructor(fn) {
        this.doneCallback = null;
        fn(this.resolve.bind(this)); // resolve will be called in another function context, must bind here
    }

    resolve(result) {
        this.doneCallback(result);
    }

    then(done) {
        this.doneCallback = done;
        return this;
    }
}

function test() {
    return new MyPromise(function (successResolve) {
        setTimeout(function () {
            console.log(100);
            successResolve(1);
        }, 1000);
    });
}

test().then((d) => {
    console.log('done' + d);
});

Added Promise chain.

class MyPromise {
    constructor(fn) {
        this.doneList = [];
        fn(this.resolve.bind(this)); // resolve will be called in another function context, must bind here
    }

    resolve(result) {
        var self = this;
        setTimeout(function () {
            self.doneList.forEach(function (fulfill) {
                fulfill(result);
            });
        }, 0);
    }

    then(done) {
        this.doneList.push(done);
        return this;
    }
}

function test() {
    return new MyPromise(function (successResolve) {
        setTimeout(function () {
            successResolve(1);
        }, 1000);
    });
}

test().then((d) => {
    console.log('step1: ' + d);
}).then(_ => {
    console.log('step2:');
}).then(m => {
    console.log('step3: ' + m);
});