次のようにコードがある注意事項
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>变量const</title>
</head>
<body>
</body>
<script>
// const定义的是常量,定义的时候必须有值，不能后赋值，且后续不能更改
</script>
<script>
const a = 12;
a = 17; //报错信息Assignment to constant variable.
console.log(a)
const b; //报错信息Missing initializer in const declaration
b = 12;
console.log(b)
</script>
<script>
const arr = ['1', '2'];
arr[0] = '3';
console.log(arr) //['3','2']
// const arr=['1','2'];
// arr.push('3')
// console.log(arr) //['1','2','3']
</script>
<script>
// const arr = Object.freeze(['1', '2']);
// arr.push('3') //报错Cannot add property 2, object is not extensible
// console.log(arr)
</script>
<script>
//对象是引用 可更改里面的值 如果是普通常量不可更改
const person = {
name: '小仙女',
age: 12,
sex: '女'
}
person.name = '小小小';
console.log(person) //{name: "小小小", age: 12, sex: "女"}
</script>
</html>