第十三天：async的详细使用
<h4>async</h4>
<pre><code>简单实例1：
async function fn(){
return 1
}
fn.then(alert)
实例2:返回Promise
async function fn(){
return Promise.resolve(1)
}
fn.then(alert)
实例3：等待返回
async function f() {
let promise = new Promise((resolve, reject) => {
setTimeout(() => resolve("done!"), 1000)
});
let result = await promise; // 等待promise完成然后返回
alert(result); // "done!"
}
f();
实例4：class
class Thenable {
constructor(num) {
this.num = num;
}
then(resolve, reject) {
alert(resolve);
// resolve with this.num*2 after 1000ms
setTimeout(() => resolve(this.num * 2), 1000); // (*)
}
};
async function f() {
// waits for 1 second, then result becomes 2
let result = await new Thenable(1);
alert(result); //2
}
f();
实例5：与class的调用
class Waiter {
async wait() {
return await Promise.resolve(1);
}
}
new Waiter()
.wait()
.then(alert); // 1
实例6：调用函数
async function wait() {
await new Promise(resolve => setTimeout(resolve, 1000));
return 10;
}
function fn() {
// shows 10 after 1 second
wait().then( result => {
return console.log(result) ; //10
});
}
fn();
//实例7：等待4秒然后返回
async function doubleAndAdd(a,b){
a = await doubleAfter1Sec(a) ;
b = await doubleAfter1Sec(b) ;
return a + b ;
}
function doubleAfter1Sec(param){
return new Promise( resolve => {
setTimeout(() => resolve(param * 2),2000)
})
}
doubleAndAdd(1,2).then(console.log)</code></pre>
<p>链接：<a href="https://blog.csdn.net/u012863664/article/details/78320977">https://blog.csdn.net/u012863664/article/details/78320977</a></p>