time-to-botec/squiggle/node_modules/@stdlib/utils/map-keys/README.md

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@license Apache-2.0
Copyright (c) 2018 The Stdlib Authors.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
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# mapKeys
> Map keys from one object to a new object having the same values.
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## Usage
```javascript
var mapKeys = require( '@stdlib/utils/map-keys' );
```
#### mapKeys( obj, transform )
Map keys from one `object` to a new `object` having the same values.
```javascript
function transform( key, value ) {
return key + value;
}
var obj1 = {
'a': 1,
'b': 2
};
var obj2 = mapKeys( obj1, transform );
// returns { 'a1': 1, 'b2': 2 }
```
The `transform` function is provided three arguments:
- `key`: object key
- `value`: object value corresponding to `key`
- `obj`: the input object
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## Notes
- Key iteration order is **not** guaranteed, as `object` key enumeration is not specified according to the [ECMAScript specification][ecma-262-for-in]. In practice, however, most engines use insertion order to sort an `object`'s keys, thus allowing for deterministic return values.
- The function only maps **own** properties. Hence, the function does **not** map inherited properties.
- The function **shallow** copies key values.
- The value returned by a `transform` function should be a value which can be serialized as an `object` key.
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## Examples
<!-- eslint no-undef: "error" -->
```javascript
var mapKeys = require( '@stdlib/utils/map-keys' );
function transform( key, value ) {
return key + ':' + value;
}
var obj1 = {
'a': 'beep',
'b': 'boop',
'c': 'foo',
'd': 'bar'
};
var obj2 = mapKeys( obj1, transform );
console.dir( obj2 );
// => { 'a:beep': 'beep', 'b:boop': 'boop', 'c:foo': 'foo', 'd:bar': 'bar' }
```
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[ecma-262-for-in]: http://www.ecma-international.org/ecma-262/5.1/#sec-12.6.4
</section>
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