javascript严格模式

设立"严格模式"的目的，主要有以下几个：

　　1. 消除Javascript语法的一些不合理、不严谨之处，减少一些怪异行为;

　　2. 消除代码运行的一些不安全之处，保证代码运行的安全；

　　3. 提高编译器效率，增加运行速度；

　　4. 为未来新版本的Javascript做好铺垫。

严格模式下，变量都必须先用var命令声明，然后再使用。

test_163:/home/exenode/es6 # more mytest.js 
class Animal{
        constructor(name){
                this.name = name;
        }

        sayName(){
                console.log('My name is ' + this.name);
        }

}

class Programmer extends Animal{
        constructor(name){
                super(name);
        }

        program(){
                console.log("I'm coding...");
        }

}

var animal = new Animal('dummy');

wayou = new Programmer('wyou');

animal.sayName();
wayou.sayName();

wayou.program();
test_163:/home/exenode/es6 # 
test_163:/home/exenode/es6 # node mytest.js 
/home/exenode/es6/mytest.js:1
(function (exports, require, module, __filename, __dirname) { class Animal{
                                                              ^^^^^

SyntaxError: Block-scoped declarations (let, const, function, class) not yet supported outside strict mode
    at exports.runInThisContext (vm.js:53:16)
    at Module._compile (module.js:414:25)
    at Object.Module._extensions..js (module.js:442:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:313:12)
    at Function.Module.runMain (module.js:467:10)
    at startup (node.js:136:18)
    at node.js:963:3

修改如下：

test_163:/home/exenode/es6 # more mytest.js 
'use strict';
class Animal{
        constructor(name){
                this.name = name;
        }

        sayName(){
                console.log('My name is ' + this.name);
        }

}

class Programmer extends Animal{
        constructor(name){
                super(name);
        }

        program(){
                console.log("I'm coding...");
        }

}

var animal = new Animal('dummy');

var wayou = new Programmer('wyou');

animal.sayName();
wayou.sayName();

wayou.program();
test_163:/home/exenode/es6 # 
test_163:/home/exenode/es6 # node mytest.js 
My name is dummy
My name is wyou
I'm coding...
test_163:/home/exenode/es6 #