> Returns true if a value is any of the object types: array, regexp, plain object, function or date. This is useful for determining if a value can be extended, e.g. "can the value have keys?"
## Install
Install with [npm](https://www.npmjs.com/)
```sh
$ npm i is-extendable --save
```
## Usage
```js
var isExtendable = require('is-extendable');
```
Returns true if the value is any of the following:
*`array`
*`regexp`
*`plain object`
*`function`
*`date`
*`error`
## Notes
All objects in JavaScript can have keys, but it's a pain to check for this, since we ether need to verify that the value is not `null` or `undefined` and:
* the value is not a primitive, or
* that the object is an `object`, `function`
Also note that an `extendable` object is not the same as an [extensible object](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/isExtensible), which is one that (in es6) is not sealed, frozen, or marked as non-extensible using `preventExtensions`.
## Related projects
* [assign-deep](https://github.com/jonschlinkert/assign-deep): Deeply assign the enumerable properties of source objects to a destination object.
* [extend-shallow](https://github.com/jonschlinkert/extend-shallow): Extend an object with the properties of additional objects. node.js/javascript util.
* [isobject](https://github.com/jonschlinkert/isobject): Returns true if the value is an object and not an array or null.
* [is-plain-object](https://github.com/jonschlinkert/is-plain-object): Returns true if an object was created by the `Object` constructor.
* [is-equal-shallow](https://github.com/jonschlinkert/is-equal-shallow): Does a shallow comparison of two objects, returning false if the keys or values differ.
* [kind-of](https://github.com/jonschlinkert/kind-of): Get the native type of a value.
## Running tests
Install dev dependencies:
```sh
$ npm i -d && npm test
```
## Contributing
Pull requests and stars are always welcome. For bugs and feature requests, [please create an issue](https://github.com/jonschlinkert/is-extendable/issues/new)
