async也是处理异步的,是promise的扩展
语法:
let p1 = new Promise((resolve,reject) => {
setTimeout(()=>{
resolve('1.异步')
},3000)
})
let p2 = new Promise((resolve,reject) => {
setTimeout(()=>{
resolve('2.异步')
},800)
})
let p3 = new Promise((resolve,reject) => {
setTimeout(()=>{
resolve('3.异步')
},1500)
})
async function as()
{
let result = await p2 // 等待p2执行
console.log(result)
}
as() // 输出 2.异步
let as = async()=>{
let result = [await p1, await p2, await p3]
console.log(result)
}
as() // 输出 [ '1.异步', '2.异步', '3.异步' ]
注意: 返回的是一个promise对象
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