105 lines
2.2 KiB
Markdown
105 lines
2.2 KiB
Markdown
---
|
|
id: 598f48a36c8c40764b4e52b3
|
|
title: Prevent Object Mutation
|
|
challengeType: 1
|
|
forumTopicId: 301207
|
|
dashedName: prevent-object-mutation
|
|
---
|
|
|
|
# --description--
|
|
|
|
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.
|
|
|
|
Any attempt at changing the object will be rejected, with an error thrown if the script is running in strict mode.
|
|
|
|
```js
|
|
let obj = {
|
|
name:"FreeCodeCamp",
|
|
review:"Awesome"
|
|
};
|
|
Object.freeze(obj);
|
|
obj.review = "bad";
|
|
obj.newProp = "Test";
|
|
console.log(obj);
|
|
```
|
|
|
|
The `obj.review` and `obj.newProp` assignments will result in errors, because our editor runs in strict mode by default, and the console will display the value `{ name: "FreeCodeCamp", review: "Awesome" }`.
|
|
|
|
# --instructions--
|
|
|
|
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.
|
|
|
|
# --hints--
|
|
|
|
You should not replace the `const` keyword.
|
|
|
|
```js
|
|
(getUserInput) => assert(getUserInput('index').match(/const/g));
|
|
```
|
|
|
|
`MATH_CONSTANTS` should be a constant variable (by using `const`).
|
|
|
|
```js
|
|
(getUserInput) =>
|
|
assert(getUserInput('index').match(/const\s+MATH_CONSTANTS/g));
|
|
```
|
|
|
|
You should not change the original declaration of `MATH_CONSTANTS`.
|
|
|
|
```js
|
|
(getUserInput) =>
|
|
assert(
|
|
getUserInput('index').match(
|
|
/const\s+MATH_CONSTANTS\s+=\s+{\s+PI:\s+3.14\s+};/g
|
|
)
|
|
);
|
|
```
|
|
|
|
`PI` should equal `3.14`.
|
|
|
|
```js
|
|
assert(PI === 3.14);
|
|
```
|
|
|
|
# --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();
|
|
```
|
|
|
|
# --solutions--
|
|
|
|
```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();
|
|
```
|