1、callback回调地狱

function ajax(fn) { setTimeout(()=> { console.log(‘你好‘) fn() }, 1000)}ajax(() => { console.log(‘执行结束‘) ajax(()=>{ console.log(‘执行结束‘) ajax(()=>{ console.log(‘执行结束‘) ajax(()=>{ console.log(‘执行结束‘) }) }) })})

2、promise解决回调地狱

function delay(word) { return new Promise((resolve, reject) => { setTimeout(()=>{ resolve(word) }, 2000) })}delay(‘孙悟空‘) .then((word)=>{ console.log(word) return delay(‘猪八戒‘) }) .then((word)=>{ console.log(word) return delay(‘沙悟净‘) }) .then((word) => { console.log(word) }) .catchconsole.log(‘执行结束‘)

3、async+await优雅处理异步

function delay(word) { return new Promise((resolve, reject) => { setTimeout(()=>{ resolve(word) }, 2000) })}async function start() { const word1 = await delay(‘孙悟空‘) console.log(word1) const word2 = await delay(‘猪八戒‘) console.log(word2) const word3 = await delay(‘沙悟净‘) console.log(word3)}
start()