ee1e8abd87
* feat(tools): add seed/solution restore script * chore(curriculum): remove empty sections' markers * chore(curriculum): add seed + solution to Chinese * chore: remove old formatter * fix: update getChallenges parse translated challenges separately, without reference to the source * chore(curriculum): add dashedName to English * chore(curriculum): add dashedName to Chinese * refactor: remove unused challenge property 'name' * fix: relax dashedName requirement * fix: stray tag Remove stray `pre` tag from challenge file. Signed-off-by: nhcarrigan <nhcarrigan@gmail.com> Co-authored-by: nhcarrigan <nhcarrigan@gmail.com>
104 lines
2.1 KiB
Markdown
104 lines
2.1 KiB
Markdown
---
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id: 598f48a36c8c40764b4e52b3
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title: Prevent Object Mutation
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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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As seen in the previous challenge, `const` declaration alone doesn't really protect your data from mutation. To ensure your data doesn't change, JavaScript provides a function `Object.freeze` to prevent data mutation.
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Once the object is frozen, you can no longer add, update, or delete properties from it. Any attempt at changing the object will be rejected without an error.
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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"; // will be ignored. Mutation not allowed
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obj.newProp = "Test"; // will be ignored. Mutation not allowed
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console.log(obj);
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// { name: "FreeCodeCamp", review:"Awesome"}
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```
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# --instructions--
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In this challenge you are going to use `Object.freeze` to prevent mathematical constants from changing. You need to freeze the `MATH_CONSTANTS` object so that no one is able to alter the value of `PI`, add, or delete properties.
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# --hints--
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You should not replace `const` keyword.
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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` should be a constant variable (by using `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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You should not change original `MATH_CONSTANTS`.
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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` should equal `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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