ES6 const声明常量与es5定义常量对比

const PI = 3.14;
PI = 4;//error

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image.png

es5声明常量

var obj ={
  aa : 1,
  bb: "abc"
};
Object.defineProperty(obj,"cc",{value:"testcc",writable:false});
console.log(obj.cc);//testcc
obj.cc=123;
console.log(obj.cc);//testcc

image.png

Object.defineProperty(window,"PI",{value:"3.1415",writable:false});
console.log(PI);//3.1415
PI=4;
console.log(PI);//3.1415