Promise 手写

Promise.resolve = function (value) {
    return new Promise((resolve, reject) => {
        if (value instanceof Promise) {
            value.then(v => {
                resolve(v);
            }, r => {
                reject(r);
            })
        } else {
            resolve(value);
        }
    })
}
Promise.reject = function (value) {
    return new Promise((resolve, reject) => {
        reject(value);
    })
}
Promise.all = function (promises) {
    return new Promise((resolve, reject) => {
        let count = 0;
        let arr = [];
        for (let i = 0; i < promises.length; i++) {
            promises[i].then(v => {
                count++;
                arr[i] = v;
                if (count === promises.length) {
                    resolve(arr);
                }
            }, r => {
                reject(r);
            });
        }
    })
}
Promise.race = function (promises) {
    return new Promise((resolve,reject) => {
        for(let i =0;i<promises.length;i++){
            promises[i].then(v => {
                resolve(v);
            }, r => {
                reject(r);
            })
        }
    })
}