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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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dashedName: use-the-rest-parameter-with-function-parameters
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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
function howMany(...args) {
return "You have passed " + args.length + " arguments.";
}
console.log(howMany(0, 1, 2)); // You have passed 3 arguments.
console.log(howMany("string", null, [1, 2, 3], { })); // You have passed 4 arguments.
```
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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.
# --instructions--
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--
The result of `sum(0,1,2)` should be 3
```js
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
assert(sum(1, 2, 3, 4) === 10);
```
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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
assert(sum() === 0);
```
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`sum` should be an arrow function which uses the rest parameter syntax (`...`) on the `args` parameter.
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```js
assert(__helpers.removeWhiteSpace(code).match(/sum=\(\.\.\.args\)=>/));
```
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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) => {
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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# --solutions--
```js
const sum = (...args) => {
return args.reduce((a, b) => a + b, 0);
}
```