<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>const命令</title>
<script src="../../../vendor/traceur.js"></script>
<script src="../../../vendor/bootstrap.js"></script>
<script type="text/traceur">
const Pi = 3.1415926535;//只能赋一次值
console.log(Pi);
Pi = 3; // Pi is read-only -- Error
console.log(Pi);
const Pi = 3.1415926535;
console.log(Pi); //3.1415926535
console.log(5 * Pi);//15.7079632675
if (true) {
const Pi = 3.14159265;
};
console.log(Pi); //Pi is not defined
var Pi = 88;
if (true) {
console.log(Pi); //undefined
const Pi = 3.14159265;
console.log(s);
};
</script>
</head>
<body>
</body>
</html>
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>const不可重复声明</title>
<script src="../../../vendor/traceur.js"></script>
<script src="../../../vendor/bootstrap.js"></script>
<script type="text/traceur">
{
var a = 100;
const a = 200;
console.log(a);//报错，局部不可重复声明
}
const person = {};//person是地址
person.name = "Zhangsan";
person.age = 30;
console.log(person.name); //Zhangsan
console.log(person.age); //30
console.log(person); //Object {name: "Zhangsan", age: 30}
person = {}; //person is read-only
</script>
</head>
<body>
</body>
</html>
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>const数组</title>
<script src="../../../vendor/traceur.js"></script>
<script src="../../../vendor/bootstrap.js"></script>
<script type="text/traceur">
const arr = [];
console.log(arr);//[]
console.log(arr.length);//0
console.log("------");
arr.push("Hello world!");
console.log(arr);//["Hello world!"]
console.log(arr.length);//1
console.log("------");
arr.length = 0;//清空数组
console.log(arr);//[]
console.log(arr.length);
console.log("------");
// 错误用法
arr = ["Hello Everyone!"];
const person = Object.freeze({kk:'kk'});//const对象冻结，对象里面的属性都不能改变
person.name = "Zhangsan";
person.age = 30;
console.log(person.kk); //kk
console.log(person.name); //undefined
console.log(person.age); //undefined
console.log(person); //Object {kk: "kk"}
const person = Object.freeze({//属性只读
name: "Zhangsan",
age : 30
});
console.log(person.name); //Zhangsan
console.log(person.age); //30
console.log(person); //Object
//冻结函数
var constantize = (obj) => {
Object.freeze(obj);
Object.keys(obj).forEach( (key, value) => {
if ( typeof obj[key] === 'object' ) {
constantize( obj[key] );//key也冻结
};
});
};
</script>
</head>
<body>
</body>
</html>
