# map-visit [](https://www.npmjs.com/package/map-visit) [](https://npmjs.org/package/map-visit) [](https://npmjs.org/package/map-visit) [](https://travis-ci.org/jonschlinkert/map-visit)
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> Map `visit` over an array of objects.
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## Install
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Install with [npm](https://www.npmjs.com/):
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```sh
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$ npm install --save map-visit
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```
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## Usage
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```js
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var mapVisit = require('map-visit');
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```
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## What does this do?
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**Assign/Merge/Extend vs. Visit**
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Let's say you want to add a `set` method to your application that will:
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* set key-value pairs on a `data` object
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* extend objects onto the `data` object
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* extend arrays of objects onto the data object
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**Example using `extend`**
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Here is one way to accomplish this using Lo-Dash's `extend` (comparable to `Object.assign`):
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```js
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var _ = require('lodash');
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var obj = {
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data: {},
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set: function (key, value) {
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if (Array.isArray(key)) {
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_.extend.apply(_, [obj.data].concat(key));
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} else if (typeof key === 'object') {
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_.extend(obj.data, key);
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} else {
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obj.data[key] = value;
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}
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}
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};
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obj.set('a', 'a');
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obj.set([{b: 'b'}, {c: 'c'}]);
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obj.set({d: {e: 'f'}});
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console.log(obj.data);
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//=> {a: 'a', b: 'b', c: 'c', d: { e: 'f' }}
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```
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The above approach works fine for most use cases. However, **if you also want to emit an event** each time a property is added to the `data` object, or you want more control over what happens as the object is extended, a better approach would be to use `visit`.
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**Example using `visit`**
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In this approach:
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* when an array is passed to `set`, the `mapVisit` library calls the `set` method on each object in the array.
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* when an object is passed, `visit` calls `set` on each property in the object.
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As a result, the `data` event will be emitted every time a property is added to `data` (events are just an example, you can use this approach to perform any necessary logic every time the method is called).
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```js
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var mapVisit = require('map-visit');
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var visit = require('object-visit');
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var obj = {
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data: {},
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set: function (key, value) {
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if (Array.isArray(key)) {
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mapVisit(obj, 'set', key);
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} else if (typeof key === 'object') {
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visit(obj, 'set', key);
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} else {
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// simulate an event-emitter
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console.log('emit', key, value);
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obj.data[key] = value;
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}
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}
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};
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obj.set('a', 'a');
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obj.set([{b: 'b'}, {c: 'c'}]);
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obj.set({d: {e: 'f'}});
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obj.set({g: 'h', i: 'j', k: 'l'});
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console.log(obj.data);
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//=> {a: 'a', b: 'b', c: 'c', d: { e: 'f' }, g: 'h', i: 'j', k: 'l'}
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// events would look something like:
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// emit a a
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// emit b b
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// emit c c
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// emit d { e: 'f' }
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// emit g h
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// emit i j
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// emit k l
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```
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## About
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### Related projects
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* [collection-visit](https://www.npmjs.com/package/collection-visit): Visit a method over the items in an object, or map visit over the objects… [more](https://github.com/jonschlinkert/collection-visit) | [homepage](https://github.com/jonschlinkert/collection-visit "Visit a method over the items in an object, or map visit over the objects in an array.")
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* [object-visit](https://www.npmjs.com/package/object-visit): Call a specified method on each value in the given object. | [homepage](https://github.com/jonschlinkert/object-visit "Call a specified method on each value in the given object.")
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### Contributing
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Pull requests and stars are always welcome. For bugs and feature requests, [please create an issue](../../issues/new).
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### Contributors
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| **Commits** | **Contributor** |
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| --- | --- |
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| 15 | [jonschlinkert](https://github.com/jonschlinkert) |
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| 7 | [doowb](https://github.com/doowb) |
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### Building docs
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_(This project's readme.md is generated by [verb](https://github.com/verbose/verb-generate-readme), please don't edit the readme directly. Any changes to the readme must be made in the [.verb.md](.verb.md) readme template.)_
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To generate the readme, run the following command:
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```sh
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$ npm install -g verbose/verb#dev verb-generate-readme && verb
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```
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### Running tests
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Running and reviewing unit tests is a great way to get familiarized with a library and its API. You can install dependencies and run tests with the following command:
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```sh
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$ npm install && npm test
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```
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### Author
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**Jon Schlinkert**
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* [github/jonschlinkert](https://github.com/jonschlinkert)
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* [twitter/jonschlinkert](https://twitter.com/jonschlinkert)
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### License
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Copyright © 2017, [Jon Schlinkert](https://github.com/jonschlinkert).
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Released under the [MIT License](LICENSE).
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***
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_This file was generated by [verb-generate-readme](https://github.com/verbose/verb-generate-readme), v0.5.0, on April 09, 2017._
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