2021-05-05 10:13:49 -07:00
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---
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id: 598f48a36c8c40764b4e52b3
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title: 防止對象改變
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challengeType: 1
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forumTopicId: 301207
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dashedName: prevent-object-mutation
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---
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# --description--
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通過之前的挑戰可以看出,`const` 聲明並不會真的保護數據不被改變。 爲了確保數據不被改變,JavaScript 提供了一個函數 `Object.freeze`。
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2021-09-18 11:22:53 -07:00
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任何更改對象的嘗試都將被拒絕,如果腳本在嚴格模式下運行,將拋出錯誤。
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2021-05-05 10:13:49 -07:00
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```js
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let obj = {
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name:"FreeCodeCamp",
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review:"Awesome"
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};
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Object.freeze(obj);
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obj.review = "bad";
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obj.newProp = "Test";
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console.log(obj);
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```
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2021-09-18 11:22:53 -07:00
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`obj.review` 和 `obj.newProp` 賦值將導致錯誤,因爲我們的編輯器默認在嚴格模式下運行,控制檯將顯示值 `{ name: "FreeCodeCamp", review: "Awesome" }`。
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2021-05-05 10:13:49 -07:00
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# --instructions--
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在這個挑戰中,你將使用 `Object.freeze` 來防止數學常量被改變。 你需要凍結 `MATH_CONSTANTS` 對象,使得沒有人可以改變 `PI` 的值,或增加或刪除屬性。
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# --hints--
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不要替換 `const` 關鍵字。
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```js
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(getUserInput) => assert(getUserInput('index').match(/const/g));
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```
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`MATH_CONSTANTS` 應該爲一個常量(使用 `const`)。
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```js
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(getUserInput) =>
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assert(getUserInput('index').match(/const\s+MATH_CONSTANTS/g));
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```
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不要改變 `MATH_CONSTANTS` 的原始聲明。
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```js
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(getUserInput) =>
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assert(
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getUserInput('index').match(
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/const\s+MATH_CONSTANTS\s+=\s+{\s+PI:\s+3.14\s+};/g
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)
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);
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```
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`PI` 應等於 `3.14`。
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```js
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assert(PI === 3.14);
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```
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# --seed--
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## --seed-contents--
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```js
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function freezeObj() {
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const MATH_CONSTANTS = {
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PI: 3.14
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};
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// Only change code below this line
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// Only change code above this line
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try {
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MATH_CONSTANTS.PI = 99;
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} catch(ex) {
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console.log(ex);
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}
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return MATH_CONSTANTS.PI;
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}
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const PI = freezeObj();
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```
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# --solutions--
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```js
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function freezeObj() {
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const MATH_CONSTANTS = {
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PI: 3.14
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};
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Object.freeze(MATH_CONSTANTS);
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try {
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MATH_CONSTANTS.PI = 99;
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} catch(ex) {
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console.log(ex);
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}
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return MATH_CONSTANTS.PI;
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}
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const PI = freezeObj();
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```
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