<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>

<body>
    <script>
        //使用settimeout
        new Promise((resolve, reject) => {
            setTimeout(() => {
                resolve()
            }, 2000)
        }).then(() => {
            console.log('hello world')
            console.log('hello world')
            console.log('hello world')
            console.log('hello world')
            return new Promise((resolve, reject) => {
                setTimeout(() => {
                    resolve()
                }, 1000)
            })
        }).then(() => {
            console.log('hello world')
            console.log('hello world')
            console.log('hello world')
            console.log('hello world')

        })
    </script>
</body>

</html>

运行结果