js setTimeout和setInterval区别

1、区别
2、示例代码
<!DOCTYPE html>
<html lang="zh">

    <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>js setTimeout和setInterval区别</title>
    </head>

    <body>
        <script type="text/javascript">
            let scriptBegin = Date.now();
            //fun1();
            fun2();
            //需要执行20ms的程序
            function act(functionName) {
                console.log(functionName, Date.now() - scriptBegin);
                let begin = Date.now();
                while(Date.now() - begin < 20);
            }
            //            function fun1 () {
            //                let fun3 = ()=>{act('fun3')}
            //                setTimeout(fun3,20);
            //                act('fun1')
            //            }
            function fun2() {
                act('fun2-1')
                let fun4 = () => {
                    act('fun4')
                }
                setInterval(fun4, 20);
                act('fun2-2')
            }
        </script>
    </body>

</html>
注：可以分别执行fun1和fun2查看执行顺序。