39 lines
1.3 KiB
Markdown
39 lines
1.3 KiB
Markdown
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---
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title: Rest Parameters
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---
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## Rest Parameters
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In ES6, the rest paramter syntax `...` allows you to gather up an indefinite number of arguments into an array.
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Even though they look the same, it does the opposite of the spread operator, which takes every item from an iterable and spreads them out into their individual values.
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### Syntax
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```js
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function myFunc(...args) {
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console.log(args);
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}
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myFunc( 1, 2, 3, 4, 5); // [1,2,3,4,5]
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```
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You can prefix a function's last parameter with `...` when you want to do something with the initial paramters and then treat all of the remaining parameters differently.
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```js
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function convertCurrency(rate, fee, ...amounts) {
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return amounts.map(amount => (amount * rate) + fee);
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}
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convertCurrency(0.89, 2.5, 100, 250, 75, 150, 300); // [ 91.5, 225, 69.25, 136, 269.5 ]
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```
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The `...` lets you gather up the rest of the arguments, if there are any, into an array.
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### The difference between rest parameters and the arguments object
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`arguments` is an array-like object, available inside functions, that contains the arguments passed to those functions. It's called "array-like" because it doesn't have all of an array's built in methods, such as `.forEach()` and `.map()`.
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The rest parameters are an array, with all of the array methods included.
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