3.预定义字符

    <script>
        var str = "_f.'-=sdhhfhlsjdjk72894k432843j3882";
        // \d表示数字相当于[0-9]
        var reg = /\d/g;
        console.log(str.replace(reg,"^"));
        // \w表示数字字母下划线
        console.log(str.replace(/\w/g,"^"));
        // .代表所有字符和符号
        console.log(str.replace(/./g,"^"));
    </script>