88 lines
2.2 KiB
Markdown
88 lines
2.2 KiB
Markdown
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---
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id: 587d7b87367417b2b2512b42
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title: Mutate an Array Declared with const
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challengeType: 1
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forumTopicId: 301206
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dashedName: mutate-an-array-declared-with-const
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---
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# --description--
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The `const` declaration has many use cases in modern JavaScript.
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Some developers prefer to assign all their variables using `const` by default, unless they know they will need to reassign the value. Only in that case, they use `let`.
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However, it is important to understand that objects (including arrays and functions) assigned to a variable using `const` are still mutable. Using the `const` declaration only prevents reassignment of the variable identifier.
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```js
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const s = [5, 6, 7];
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s = [1, 2, 3]; // throws error, trying to assign a const
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s[2] = 45; // works just as it would with an array declared with var or let
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console.log(s); // returns [5, 6, 45]
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```
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As you can see, you can mutate the object `[5, 6, 7]` itself and the variable `s` will still point to the altered array `[5, 6, 45]`. Like all arrays, the array elements in `s` are mutable, but because `const` was used, you cannot use the variable identifier `s` to point to a different array using the assignment operator.
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# --instructions--
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An array is declared as `const s = [5, 7, 2]`. Change the array to `[2, 5, 7]` using various element assignments.
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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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`s` should be a constant variable (by using `const`).
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```js
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(getUserInput) => assert(getUserInput('index').match(/const\s+s/g));
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```
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You should not change the original array declaration.
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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+s\s*=\s*\[\s*5\s*,\s*7\s*,\s*2\s*\]\s*;?/g
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)
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);
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```
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`s` should be equal to `[2, 5, 7]`.
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```js
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assert.deepEqual(s, [2, 5, 7]);
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```
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# --seed--
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## --seed-contents--
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```js
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const s = [5, 7, 2];
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function editInPlace() {
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// Only change code below this line
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// Using s = [2, 5, 7] would be invalid
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// Only change code above this line
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}
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editInPlace();
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```
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# --solutions--
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```js
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const s = [5, 7, 2];
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function editInPlace() {
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s[0] = 2;
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s[1] = 5;
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s[2] = 7;
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}
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editInPlace();
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```
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