Promise

20181101補充:

Promise A+規範:

https://promisesaplus.com/

 

Promise的語法:

new Promise(resolve,reject){

 

   。。。。執行代碼

   

}.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爲promise對象) 

Promise.all(iterable) 方法返回一個 Promise 實例，此實例在 iterable 參數內全部的 promise 都「完成（resolved）」或參數中不包含 promise 時回調完成（resolve）；若是參數中  promise 有一個失敗（rejected），此實例回調失敗（rejecte），失敗緣由的是第一個失敗 promise 的結果。

 

Promise.race：

Promise.race(iterable) 方法返回一個 promise ，並伴隨着 promise對象解決的返回值或拒絕的錯誤緣由, 只要 iterable 中有一個 promise 對象"解決(resolve)"或"拒絕(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"