javascript中怎么将值转为字符串类型

<script>

    // 转换成string类型，三种方式：变量.toString(); String('值'); 使用'+'拼接一个字符串;

    // number类型转string

    // .toString()

    var num =123;

    num = num.toString();

    console.log(typeof num);//返回的是string;

    // String()

    var num2 =50;

    var str1 = String(num2);

    console.log(typeof str1);//返回string

    // 拼接字符串

    var num3 =60;

    var str1s = num3 +'';

    console.log(str1s);

    console.log(typeof str1s);//返回string

    // 常量：

    // .toString()

    // 123.toString(); //编辑器报错，说明没有这种写法

    // String()

    var str1 = String(123);

    console.log(typeof str1);//返回string

    // boolean类型转string

    // .toString()

    var boo =false;

    boo = boo.toString();

    console.log(typeof boo);//返回的是string

    // String()

    var boo2 =true;

    var str3 = String(boo2);

    console.log(typeof str3);//返回string

    // 拼接字符串

    var boo3 =false;

    var str3s = boo3 +'';

    console.log(str3s);

    console.log(typeof str3s);//返回string

    // undefined转换成string

    // .toString()

    var und;

    und = und.toString();

    console.log(und);

    console.log(typeof und);

    //报异常： Cannot read property 'toString' of undefined

    // String()

    var und2;

    var str4 = String(und2);

    console.log(typeof str4);//返回string

    // 拼接字符串

    var nud3;

    var str4s = nud3 +'';

    console.log(str4s);

    console.log(typeof str4s);//返回string

    // null转换成string

    // .toString()

    var nul =null;

    nul = nul.toString();

    console.log(typeof nul);

    //报异常：Cannot read property 'toString' of null

    // String()

    var nul2 =null;

    var str5 = String(nul2);

    console.log(typeof str5);//返回string

    // 拼接字符串

    var nul3;

    var str5s = nul3 +'';

    console.log(str5s);

    console.log(typeof str5s);//返回string

    // 复杂数据类型转字符串

    // 数组调用toString();

    var arr = [

        'hello',

        'world'

    ];

    arr = arr.toString();

    console.log(arr);//输出结果为“hello,world”;

    console.log(typeof arr);//返回的是string

    // 数组调用String();

    var ars = [

        'jack',

        'rose'

    ];

    ars = toString(ars);

    console.log(ars);//输出结果是[object Undefined]

    console.log(typeof ars);//返回的是string

    // 拼接字符串

    var arr = [

        'hello',

        'world'

    ];

    arr = arr +'';

    console.log(arr);//输出结果为“hello,world”;

    console.log(typeof arr);//返回的是string

</script>