2-1 string , boolean，number之间转换

1.other—>number

        // "", "  " 转换为0
        //不为数字是为 NaN
//String转number
        var str = 'adadadada';
        var str1 = '111111';
        var str2 = '';
        var str3 = ' ';
        console.log(Number(str))//NaN
        console.log(Number(str1)) //11111
        console.log(Number(str2))//0
        console.log(Number(str3)) //0
//boolean转number
        var boo1 =true
        var boo2 =false
        console.log(Number(boo1) ) //1
        console.log(Number(boo2) ) //0
//undefined转 number 
        var y = undefined  
        console.log(Number(y))//NaN
// null转 number
        var z =null
        console.log(Number(z)) //0
//obj 转 number
        var obj={a:2,b:3}
        console.log(Number (obj)) //NaN

2.other—>string

       var num = 100
        var obj={a:2,b:3}
        var boo = true
        console.log(num+"")
        console.log(String(obj))
        console.log(boo.toString())

// 只有0 是才转换为false，其他都为true
        var num =0;
        var n = -1
        var m = 1
        console.log(Boolean(num))
        console.log(Boolean(n))
        console.log(Boolean(m))

3.other——>boolean

// number转换为boolean
        var num  = 5;
        var num1 = 0.8;
        var num2 = 0;
        var num3 = NaN;
        console.log(Boolean (num)) //true
        console.log(Boolean (num1)) //ture
        console.log(Boolean (num2)) //false
        console.log(Boolean (num3)) //false
// string转Boolean
        var str = '111111';
        var str2 = '';
        var str3 = ' ';
        console.log(str) //true
        console.log(str2) //false
        console.log(str3) //ture
//undefied 转Boolean
        var x ;
        console.log(x)  //false
//对像转Boolean都是true

4.四种转换为false

         number-->0；
        string-->""
          undefined
            NaN
            var a;
        console.log(a)
        console.log(NaN)