javaScript我学之一变量类型

本文是网易云课堂金旭亮老师的课程笔记，记录下来，以供备忘。

变量类型

只有6种 : 四种原始数据类型boolean , number, string , undefine, 其他object,function是对象

typeof,instanceof

直接看实例：

        var obj = null;        console.info(typeof obj);       //Object        var arr = [];        console.info(arr instanceof Object);   //true        console.info(arr instanceof Array);    //true

console.log(parseInt("34", 10)); //34console.log(parseInt("34s5b", 10)); //34console.log(parseInt("s", 10)); //NaNconsole.log(parseInt(3.14, 10)); //3

//numbervar value = 100; //stringvalue = "qiu"; //objectvalue = [1, 'two', 3];

               =         赋值               ==       判等               ===     严格判等var x = 42;var y = "42";console.log(x == y) //true;console.log(x === y) //false

var obj = null;if (obj === null) {alert("obj === null"); //此句将执行}else {alert("obj!=null");}alert(typeof obj); //object

undefine与null的 判等

var myVar;//trueconsole.log(typeof myVar === "undefined");console.log(myVar === undefined); var myVar2 = null;console.log(typeof myVar2); //object//true;console.log(myVar2 == null);console.log(myVar2 === null); //trueconsole.info(myVar == myVar2); //undefine == null; 是true//falseconsole.info(myVar === myVar2); //undefine === null; 是false