20181101补充:
Promise A+规范:
https://promisesaplus.com/
Promise的语法:
new Promise(resolve,reject){
。。。。执行代码
}.then
(onFulfilled, onRejected)let promiseToCleanTheRoom = new Promise(function(resolve,reject){
//cleaning the room
let isClean = false;
if(isClean){
resolve('Clean');
}else{
reject('not Clean');
}
});
promiseToCleanTheRoom.then(function(fromResolve){
console.log('the room is' + fromResolve);
}).catch(function(fromReject){
console.log('the room is' + fromReject);
});
resolve:
reject:
three seperate Promises:
Promise.all[ xxx,xxx,xxx]：(xxx为promise对象)
Promise.all(iterable) 方法返回一个 Promise 实例，此实例在 iterable 参数内所有的 promise 都“完成（resolved）”或参数中不包含 promise 时回调完成（resolve）；如果参数中 promise 有一个失败（rejected），此实例回调失败（rejecte），失败原因的是第一个失败 promise 的结果。
Promise.race：
Promise.race(iterable) 方法返回一个 promise ，并伴随着 promise对象解决的返回值或拒绝的错误原因, 只要 iterable 中有一个 promise 对象"解决(resolve)"或"拒绝(reject)"。
var promise1 = new Promise(function(resolve, reject) {
setTimeout(resolve, 500, 'one');
});
var promise2 = new Promise(function(resolve, reject) {
setTimeout(resolve, 100, 'two');
});
Promise.race([promise1, promise2]).then(function(value) {
console.log(value);
// Both resolve, but promise2 is faster
});
// expected output: "two"
