41 lines
1.1 KiB
Markdown
41 lines
1.1 KiB
Markdown
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---
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title: Function Length
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---
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## Function Length
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The `length` property on the function object holds the number of arguments expected by the function when called.
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```javascript
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function noArgs() { }
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function oneArg(a) { }
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console.log(noArgs.length); // 0
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console.log(oneArg.length); // 1
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```
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### ES2015 Syntax
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ES2015, or ES6 as it is commonly called, introduced the rest operator and default function parameters. Both of these additions change the way the `length` property works.
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If either the rest operator or default parameters are used in a function declaration the `length` property will only include the number of arguments before a rest operator or a default parameter.
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```javascript
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function withRest(...args) { }
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function withArgsAndRest(a, b, ...args) { }
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function withDefaults(a, b = 'I am the default') { }
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console.log(withRest.length); // 0
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console.log(withArgsAndRest.length); // 2
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console.log(withDefaults.length); // 1
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```
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More Information on `Function.length` can be found on [Mozilla's MDN Docs](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/length).
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