js中的数据类型、非运算、等值判断

1 js的数据类型

//console.log(typeof arr)，输出变量的类型var arr;                        //undefinedarr = function foo() {          //function    // body...}arr = [];               //objectarr[0] = 1;             //objectarr = null;             //objectarr = new Date();       //objectarr = "test";           //stringarr = 1;                //number

2 js空值的非运算与等值判断

var obj1;var obj2 = null;var obj3 = "";var obj4 = [];//非运算console.log(!obj1);         //trueconsole.log(!obj2);         //trueconsole.log(!obj3);         //trueconsole.log(!obj4);         //false,空数组应该判断长度console.log(obj4.length);   //0//等值判断console.log(obj1 == obj2);      //true, undefinded = nullconsole.log(obj1 === obj2);     //false, undefinded不严格等于nullconsole.log(obj2 == null);      //true, null = nullconsole.log(obj3 == "");        //trueconsole.log(obj4 == []);        //false, 空数组not equal []

3 array和object的等值判断

var arr1 = [1, 2, 3];var arr2 = [1, 2, 3];console.log(arr1 == arr2);          //falseconsole.log(arr1 == [1, 2, 3]);     //falsevar obj1 = {"a" : "1"};var obj2 = {"a" : "1"};console.log(obj1 == obj2);          //falseconsole.log(obj1 == {"a" : "1"});   //false