ES6 promise

let promise = new Promise (function (resolve, reject) {
if (true) {
resolve(value)
//异步操作成功时执行的代码
} else {
reject(error)
//异步操作失败时候执行的代码
}
})

promise.then(resolved, rejected)
// resolved和rejected分别是异步操作执行成功和失败时候回调函数，rejected回调函数是可选的
function timeout(ms) {
return new Promise((resolve, reject) => {
setTimeout(resolve, ms, ‘done‘);
});
}

timeout(100).then((value) => {
console.log(value);
});

promise.then(resolved).catch(rejected)

catch用于捕获错误

promise.all([p1, p2, p3]) //p1,p2,p3三个异步操作同时进行，只有当三个都完成的时候才返回fulfilled，只要有一个rejected就变为rejected

var p = promise.race([p1, p2, p3]) //只要p1、p2、p3中有一个实例率先改变状态，p的状态就跟着改变
promise.resolve()将对象转为promise对象
var jsPromise = Promise.resolve($.ajax(‘/whatever.json‘));

Promise.resolve(‘foo‘)
// 等价于
new Promise(resolve => resolve(‘foo‘))

promise.reject()