How to require underscore in react-native

Question

The change log of react-native mentions https://facebook.github.io/react/blog/2015/04/17/react-native-v0.4.html

NPM modules compatibility: There are a lot of libraries on NPM that do not depend on node/browser internals that would be really useful in React Native, such as superagent, underscore, ...

But It doesn't work for me. It is how I install, through package.json

# package.json

 "dependencies": {
   "react-native": "*",
   "underscore": "^1.8.3"
   ...

And I indeed see it in the npm dependecy

# npm ls
├─┬ react-native@0.8.0
|  ...
├── react-native-navbar@0.7.3
└── underscore@1.8.3

And it does work for some other react components

It is how I require

var _ = require('underscore');

But it doesn't work, _ is undefined

Answer 1

If you are using ES6 module (like in ReactNative) the correct way is to use the import statement:

import _ from 'lodash'

let text = _.isUndefined(route.rightButtonText) ? 'Default value' : route.rightButtonText;

Answer 2

I am using lodash (underscore with more stuff) like this:

1. Add this to the package.json "lodash": "^3.10.0"

2. In the component you need just write: var _ = require('lodash')

And you are set.

Here is more info on lodash if you need lodash

Answer 3

To run require successfully in React, this is what I did:

1. Install underscore.

    npm install underscore 

2. Define a dependency in package.json

    "dependencies": { "react": "^0.13.*", "underscore": "^1.8.3" } 

3. Define underscore inside the function where you want to use it.

    render() { let _ = require('underscore') let buttonStyle = _.clone(button); } 

Answer 4

I found the issue, the problem is

I do NOT use it

I just require it and try to test it in console.

When I use it in somewhere, like _.map([1, 2, 3], function(num){ return num * 3; }) anywhere.

Then I test it in console, it does require the library this time.

I am not sure this is npm require or react-native behavior ?

When you don't use a library, even you require it, it won't be required.