2018-10-10 22:03:03 +00:00
|
|
|
|
---
|
|
|
|
|
id: 598f48a36c8c40764b4e52b3
|
2021-03-15 03:20:39 +00:00
|
|
|
|
title: 防止对象改变
|
2018-10-10 22:03:03 +00:00
|
|
|
|
challengeType: 1
|
2020-08-04 07:13:35 +00:00
|
|
|
|
forumTopicId: 301207
|
2021-01-13 02:31:00 +00:00
|
|
|
|
dashedName: prevent-object-mutation
|
2018-10-10 22:03:03 +00:00
|
|
|
|
---
|
|
|
|
|
|
2020-12-16 07:37:30 +00:00
|
|
|
|
# --description--
|
|
|
|
|
|
2021-03-15 03:20:39 +00:00
|
|
|
|
通过之前的挑战可以看出,`const` 声明并不会真的保护数据不被改变。 为了确保数据不被改变,JavaScript 提供了一个函数 `Object.freeze`。
|
2020-12-16 07:37:30 +00:00
|
|
|
|
|
2021-03-15 03:20:39 +00:00
|
|
|
|
当一个对象被冻结的时候,你不能再对它的属性再进行增、删、改的操作。 任何试图改变对象的操作都会被阻止,却不会报错。
|
2020-08-04 07:13:35 +00:00
|
|
|
|
|
|
|
|
|
```js
|
|
|
|
|
let obj = {
|
|
|
|
|
name:"FreeCodeCamp",
|
|
|
|
|
review:"Awesome"
|
|
|
|
|
};
|
|
|
|
|
Object.freeze(obj);
|
2021-03-15 03:20:39 +00:00
|
|
|
|
obj.review = "bad";
|
|
|
|
|
obj.newProp = "Test";
|
2020-08-04 07:13:35 +00:00
|
|
|
|
console.log(obj);
|
|
|
|
|
```
|
|
|
|
|
|
2021-03-15 03:20:39 +00:00
|
|
|
|
`obj.review` 和 `obj.newProp` 赋值将导致错误,控制台将显示值 `{ name: "FreeCodeCamp", review: "Awesome" }`。
|
|
|
|
|
|
2020-12-16 07:37:30 +00:00
|
|
|
|
# --instructions--
|
2018-10-10 22:03:03 +00:00
|
|
|
|
|
2021-03-15 03:20:39 +00:00
|
|
|
|
在这个挑战中,你将使用 `Object.freeze` 来防止数学常量被改变。 你需要冻结 `MATH_CONSTANTS` 对象,使得没有人可以改变 `PI` 的值,或增加或删除属性。
|
2018-10-10 22:03:03 +00:00
|
|
|
|
|
2020-12-16 07:37:30 +00:00
|
|
|
|
# --hints--
|
2018-10-10 22:03:03 +00:00
|
|
|
|
|
2021-03-15 03:20:39 +00:00
|
|
|
|
不要替换 `const` 关键字。
|
2018-10-10 22:03:03 +00:00
|
|
|
|
|
2020-12-16 07:37:30 +00:00
|
|
|
|
```js
|
|
|
|
|
(getUserInput) => assert(getUserInput('index').match(/const/g));
|
2018-10-10 22:03:03 +00:00
|
|
|
|
```
|
|
|
|
|
|
2021-03-15 03:20:39 +00:00
|
|
|
|
`MATH_CONSTANTS` 应该为一个常量(使用 `const`)。
|
2018-10-10 22:03:03 +00:00
|
|
|
|
|
|
|
|
|
```js
|
2020-12-16 07:37:30 +00:00
|
|
|
|
(getUserInput) =>
|
|
|
|
|
assert(getUserInput('index').match(/const\s+MATH_CONSTANTS/g));
|
2018-10-10 22:03:03 +00:00
|
|
|
|
```
|
|
|
|
|
|
2021-03-15 03:20:39 +00:00
|
|
|
|
不要改变 `MATH_CONSTANTS` 的原始声明。
|
2018-10-10 22:03:03 +00:00
|
|
|
|
|
2020-12-16 07:37:30 +00:00
|
|
|
|
```js
|
|
|
|
|
(getUserInput) =>
|
|
|
|
|
assert(
|
|
|
|
|
getUserInput('index').match(
|
|
|
|
|
/const\s+MATH_CONSTANTS\s+=\s+{\s+PI:\s+3.14\s+};/g
|
|
|
|
|
)
|
|
|
|
|
);
|
|
|
|
|
```
|
2018-10-10 22:03:03 +00:00
|
|
|
|
|
2021-03-15 03:20:39 +00:00
|
|
|
|
`PI` 应等于 `3.14`。
|
2018-10-10 22:03:03 +00:00
|
|
|
|
|
|
|
|
|
```js
|
2020-12-16 07:37:30 +00:00
|
|
|
|
assert(PI === 3.14);
|
2018-10-10 22:03:03 +00:00
|
|
|
|
```
|
2020-08-04 07:13:35 +00:00
|
|
|
|
|
2021-01-13 02:31:00 +00:00
|
|
|
|
# --seed--
|
|
|
|
|
|
|
|
|
|
## --seed-contents--
|
|
|
|
|
|
|
|
|
|
```js
|
|
|
|
|
function freezeObj() {
|
|
|
|
|
const MATH_CONSTANTS = {
|
|
|
|
|
PI: 3.14
|
|
|
|
|
};
|
|
|
|
|
// Only change code below this line
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
// Only change code above this line
|
|
|
|
|
try {
|
|
|
|
|
MATH_CONSTANTS.PI = 99;
|
|
|
|
|
} catch(ex) {
|
|
|
|
|
console.log(ex);
|
|
|
|
|
}
|
|
|
|
|
return MATH_CONSTANTS.PI;
|
|
|
|
|
}
|
|
|
|
|
const PI = freezeObj();
|
|
|
|
|
```
|
|
|
|
|
|
2020-12-16 07:37:30 +00:00
|
|
|
|
# --solutions--
|
|
|
|
|
|
2021-01-13 02:31:00 +00:00
|
|
|
|
```js
|
|
|
|
|
function freezeObj() {
|
|
|
|
|
const MATH_CONSTANTS = {
|
|
|
|
|
PI: 3.14
|
|
|
|
|
};
|
|
|
|
|
Object.freeze(MATH_CONSTANTS);
|
|
|
|
|
|
|
|
|
|
try {
|
|
|
|
|
MATH_CONSTANTS.PI = 99;
|
|
|
|
|
} catch(ex) {
|
|
|
|
|
console.log(ex);
|
|
|
|
|
}
|
|
|
|
|
return MATH_CONSTANTS.PI;
|
|
|
|
|
}
|
|
|
|
|
const PI = freezeObj();
|
|
|
|
|
```
|