78 lines
1.7 KiB
Markdown
78 lines
1.7 KiB
Markdown
---
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id: 587d7b88367417b2b2512b47
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title: Use the Rest Parameter with Function Parameters
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challengeType: 1
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forumTopicId: 301221
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---
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# --description--
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In order to help us create more flexible functions, ES6 introduces the <dfn>rest parameter</dfn> for function parameters. With the rest parameter, you can create functions that take a variable number of arguments. These arguments are stored in an array that can be accessed later from inside the function.
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Check out this code:
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```js
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function howMany(...args) {
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return "You have passed " + args.length + " arguments.";
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}
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console.log(howMany(0, 1, 2)); // You have passed 3 arguments.
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console.log(howMany("string", null, [1, 2, 3], { })); // You have passed 4 arguments.
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```
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The rest parameter eliminates the need to check the `args` array and allows us to apply `map()`, `filter()` and `reduce()` on the parameters array.
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# --instructions--
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Modify the function `sum` using the rest parameter in such a way that the function `sum` is able to take any number of arguments and return their sum.
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# --hints--
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The result of `sum(0,1,2)` should be 3
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```js
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assert(sum(0, 1, 2) === 3);
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```
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The result of `sum(1,2,3,4)` should be 10
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```js
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assert(sum(1, 2, 3, 4) === 10);
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```
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The result of `sum(5)` should be 5
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```js
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assert(sum(5) === 5);
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```
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The result of `sum()` should be 0
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```js
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assert(sum() === 0);
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```
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The `sum` function should use the `...` rest parameter on the `args` parameter.
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```js
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assert(__helpers.removeWhiteSpace(code).match(/sum=\(\.\.\.args\)=>/));
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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 sum = (x, y, z) => {
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const args = [x, y, z];
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return args.reduce((a, b) => a + b, 0);
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}
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```
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# --solutions--
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```js
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const sum = (...args) => {
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return args.reduce((a, b) => a + b, 0);
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}
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```
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