一个简单的Promise[使用class]

一个简单的Promise

前置文章这一次，彻底弄懂 Promise 原理

使用class实现简单的Promise

class Promise {
    constructor(callback) {
        this.state = 'pending';
        this.value = null;
        this.error = null;
        this.successCallback = [];
        this.errorCallback = [];
        this.resolve = this.resolve.bind(this);
        this.reject = this.reject.bind(this);
        callback(this.resolve, this.reject);
    }
    resolve(value) {
        if (this.state === 'pending') {
            this.state = 'resolved';
            this.value = value;
            setTimeout(() => {
                this.successCallback.forEach((callback) => {
                    callback(this.value);
                });
            }, 0);
        }
    }
    reject(error) {
        if (this.state === 'pending') {
            this.error = error;
            this.state = 'resolved';
            setTimeout(() => {
                this.errorCallback.forEach((callback) => {
                    callback(this.error);
                });
            }, 0);
        }
    }

    then(success, fail) {
        this.successCallback.push(success);
        this.errorCallback.push(fail);
        return this;
    }
}

test case

new Promise((resolve, reject) => {
    resolve({name:'zs',age:12});
    reject({errMsg:'我错了'});
})
    .then(
        (value) => {
            console.log(value);
        },
        (error) => {
            console.log(error);
        }
    )
    .then(
        (value) => {
            console.log('第二个', value);
        },
        (error) => {
            console.log(error);
        }
    );