Javascript 严格模式use strict详解

function fn() {  "use strict";  //some code}

"use strict";var x;delete x;//报错Delete of an unqualified identifier in strict mode.（不合格的标识符）

function fn(a,a){ "use strict";  result=a+a;  console.log(result);}fn(2,4);//Duplicate parameter name not allowed in this context(重复的参数名称在此上下文中不允许)

function fn1(a,a){  "use strict";  result=a+a;  console.log(result);}fn1(2,4);//结果为8

"use strict"var x=089;console.log(x);//报错：Decimals with leading zeros are not allowed in strict mode.

fn(5);function fn(a){  "use strict";  a = 42;  // return a==arguments[0];//返回false  console.log(a);//结果为42  console.log(arguments[0]);//结果为5,严格模式下arguments[0]表示这个调用方法的第一个参数     (不再追踪  参数的变化，在函数内部，参数a被重新赋值为42，但arguments[0]仍然为5.)}

fn(5);function fn(a){  a = 42;  // return a==arguments[0];//返回true  console.log(a);//结果为42  console.log(arguments[0]);//结果为42(追踪参数变化)}

"use strict";var eval=3;//报错：Unexpected eval or arguments in strict modevar argument=6；//同样报错

"use strict";function fn(n){  if(n==0){    return 1;  }else{    return n*arguments.callee(n-1);  }}console.log(fn(5));//报错

function fn(n){//阶乘  if(n==0){    return 1;  }else{    return n*arguments.callee(n-1);  }}console.log(fn(5));//正常120

"use strict"function fn1() {  var n1= fn1.caller;  console.log(n1);}function fn2() {  fn1();}fn2();//报错

function fn1() {  var n1= fn1.caller;//此例中caller指向调用它的函数（fn2）  console.log(n1);}function fn2() {  fn1();}fn2();// 结果打印出：function fn2(){ fn1( ) };

"use strict"；with（obj）{  x；}//报错：Strict mode code may not include a with statement

with(object instance){  //代码块}eg：function Clothes(){  this.color="red";  this.size="m";  this.price="cheap";}var c1=new Clothes();with(c1){  var str="颜色："+color+"，尺寸："+size+"，价格："+price;  document.write(str);}//结果(颜色：red，尺寸：m，价格：cheap)