9.比较运算

// undefined,””,NaN,0—>false
//>,<,==返回的是boolean
//先将两边的值转换为number，再比较
//NaN和任何值做计算，结果一定是NaN

var a=true;
        var b="10";
        var c="hello";
        console.log(a>b);//Number(a)>Number(b) false
        console.log(a>c);//Number(a)>Number(b) false
        console.log(Boolean(NaN));
        //undefined
        var m;
        console.log(m);//undefined