Promise.finally
Promise.prototype.finally = function(cb) {
const P = this.constructor;
return this.then(
val => P.resolve(cb()).then(() => val),
err =>
P.resolve(cb()).then(() => {
throw err;
})
);
};
Promise.all
function promiseAll(promises) {
return new Promise((resolve, reject) => {
if (!Array.isArray(promises)) {
return reject(new TypeError("argument must be anarray"));
}
const countNum = 0;
const promiseNum = promises.length;
const resultVal = new Array(promiseNum);
for (let i = 0; i < promiseNum; i++) {
Promise.resolve(promises[i]).then(
val => {
countNum++;
resultVal[i] = val;
if (countNum === promiseNum) {
return resolve(resultVal);
}
},
err => {
return reject(err);
}
);
}
});
}
Promise.race
function race(promises) {
return new Promise((resolve, reject) => {
promises.forEach(element => {
Promise.resolve(element).then(resolve, reject);
});
});
}
