JS中的隐式类型转换

isNaN(123);         //falseisNaN("123");       //false，字符串//Number('123')  ==> isNaN(123)  ==> falseisNaN("null");      //true，字符串//Number("null")  ==> isNaN(NaN)  ==> trueisNaN(null);        //false，null对象//Number(null)  ==> isNaN(0)  ==> falseisNaN(undefined);   //true//Number(undefined)  ==> isNaN(NaN)  ==> trueisNaN("123bcd");    //true//Number("123bcd")  ==> isNaN(NaN)  ==> true

var a = '123'; a ++;     //a 124var b = 'abc'; a ++;     //b NaN; typeof(b) ==> numbervar c = + 'abc';         //c NaN; typeof(c) ==> number

var a = 1 + "123";      //"1123"var b = "abc" + 12;     //"abc12"

var a = 1/"2";      //a  0.5;typeof(a)  number

> <  >= <= == 有字符串和数字比较的，隐式的调用Number()转换成数字
//undefined ,null,"abc"都转换成NaNundefined > 0       //falseundefined < 0       //falseundefined == 0      //falsenull > 0            //falsenull < 0            //falsenull == 0           //false"abc" > 0           //false"abc" < 0           //false"abc" == 0          //false

undefined == undefined //truenull == null           //trueNaN == NaN             //false