Promise簡單使用，需要在ES6以上

 //Promise延時順序執行

var waitOne = new Promise(function(resolve, reject) {
     setTimeout(function(){ resolve(1)}, 1000);
}); 
var waitSecond = new Promise(function(resolve, reject) {
     setTimeout(function(){ resolve(1)}, 1000);
}); 
waitOne.then(function() {
    console.log("Hello"); // 1秒後輸出"Hello"
    return new Promise(function(resolve, reject) {
     setTimeout(function(){ resolve(1)}, 1000);
    });
}).then(function() {
    console.log("Hi"); // 2秒後輸出"Hi"
});

new Promise(function(resolve , reject) {
    resolve(1);
}).then(function(val) {
    console.log(val);
    return new Promise(function(resolve , reject) {
        resolve(2);
    });
}).then(function(val) {
    console.log(val);
    return new Promise(function(resolve , reject) {
        resolve(3);
    });
}).then(function(val) {
    console.log(val);
    return new Promise(function(resolve , reject) {
        resolve(4);
    });
}).then(function(val) {
    console.log(val);
});

//輸出：
//      1
//      2
//      3
//      4

setTimeout(function () {
  console.log('three');
}, 0);

Promise.resolve().then(function () {
  console.log('two');
});

console.log('one');