JS 作用域 实例分析

/*  此模块测试变量作用域 star */
var a ;
console.log(a); //undefined
function testScope0(){
    a = 10;
    console.log(a); //10
}
testScope0();
/*  此模块测试变量作用域 end */

/*  此模块测试变量作用域 star */
 var a = 100;
 console.log(a); //100

function testScope1(){
    a = 10;
    console.log(a); //10
}
testScope1();

function testScope2(){
    var a = 10;
    console.log(a); //10
}
testScope2();

function testScope3(){
    var a = 10;
    console.log(a); //10
    console.log(this.a); //100
}
testScope3();

function testScope4(){
    a = 10;
    console.log(a); //10
    console.log(this.a); //100
    var a =1000;
    console.log(a);//1000
}
testScope4();

/*  此模块测试变量作用域 end */

/*  此模块测试变量作用域 star */
var a = b = null;
var c = 1;
(function a(v){
    console.log(c); //1
    console.log(v); //1
 return a = v;
})(c)
 console.log(a); //null

var a = b = null;
var c = 1;
function otherScope(c){
    console.log(c); //1
    a = c;
    console.log(a); //1
 return a;
}
otherScope(c);
console.log(a); //1

/*  此模块测试变量作用域 end */

/*  此模块测试变量作用域 star */
var name = "window";
var obj = {
    name:"the obj",
    getName:function(){
        return this.name
    }
}
console.log(obj.getName()); //the obj
/*  此模块测试变量作用域 end */

/*  此模块测试变量作用域 star */
var name = "window";
var obj = {
    name:"the obj",
    getName:function(){
                return function(){
                    return this.name;
                }
            }
    }
console.log(obj.getName()()); //window
/*  此模块测试变量作用域 end */

/*  此模块测试变量作用域 star */
var a;
if(a in window){
 console.log("yes"); //yes
} 

if(!(a in window)){
    var a = 1;
}
console.log(a); //undefined
/*  此模块测试变量作用域 end */

 

转载于:https://www.cnblogs.com/xmyun/p/5923749.html