Using the Underscore module with Node.js

Question

I've been learning about node.js and modules, and can't seem to get the Underscore library to work properly... it seems that the first time I use a function from Underscore, it overwrites the _ object with the result of my function call. Anyone know what's going on? For example, here is a session from the node.js REPL:

Admin-MacBook-Pro:test admin$ node
> require("./underscore-min")
{ [Function]
  _: [Circular],
  VERSION: '1.1.4',
  forEach: [Function],
  each: [Function],
  map: [Function],
  inject: [Function],
  (...more functions...)
  templateSettings: { evaluate: /<%([\s\S]+?)%>/g, interpolate: /<%=([\s\S]+?)%>/g },
  template: [Function] }
> _.max([1,2,3])
3
> _.max([4,5,6])
TypeError: Object 3 has no method 'max'
    at [object Context]:1:3
    at Interface.<anonymous> (repl.js:171:22)
    at Interface.emit (events.js:64:17)
    at Interface._onLine (readline.js:153:10)
    at Interface._line (readline.js:408:8)
    at Interface._ttyWrite (readline.js:585:14)
    at ReadStream.<anonymous> (readline.js:73:12)
    at ReadStream.emit (events.js:81:20)
    at ReadStream._emitKey (tty_posix.js:307:10)
    at ReadStream.onData (tty_posix.js:70:12)
> _
3

When I make Javascript files myself and import them, they seem to be working properly. Maybe there's something special with the Underscore library?

Nimantha · Accepted Answer · 2021-10-29 17:11:46Z

195

As of today (April 30, 2012) you can use Underscore as usual on your Node.js code. Previous comments are right pointing that REPL interface (Node's command line mode) uses the "_" to hold the last result BUT on you are free to use it on your code files and it will work without a problem by doing the standard:

var _ = require('underscore');

edited Oct 29, 2021 at 17:11

Nimantha

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answered Apr 30, 2012 at 23:42

user1366860

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6 Comments

Lance Pollard Over a year ago

Note, this doesn't work if you try to globalize underscore: gist.github.com/3220108

user1366860 Over a year ago

Someone once told me that Globals are bad on all development languages. I do not see a problem having to specify var _ = require('underscore') on the modules who require it. nodejs.org/api/modules.html#modules_caching

poseid Over a year ago

What Node version does 30-apri-2012 correspond with?

user1366860 Over a year ago

April 2012 corresponds to 0.6.

Brandon Over a year ago

Erick, it's a problem if you're trying to reuse client-side code on the server side as well.

|

Mike Scott · Accepted Answer · 2011-04-17 10:07:09Z

The Node REPL uses the underscore variable to hold the result of the last operation, so it conflicts with the Underscore library's use of the same variable. Try something like this:

Admin-MacBook-Pro:test admin$ node
> _und = require("./underscore-min")
{ [Function]
  _: [Circular],
  VERSION: '1.1.4',
  forEach: [Function],
  each: [Function],
  map: [Function],
  inject: [Function],
  (...more functions...)
  templateSettings: { evaluate: /<%([\s\S]+?)%>/g, interpolate: /<%=([\s\S]+?)%>/g },
  template: [Function] }
> _und.max([1,2,3])
3
> _und.max([4,5,6])
6

micrub · Accepted Answer · 2012-02-21 20:42:50Z

29

Or :

    var _ = require('underscore')._;

answered Feb 21, 2012 at 20:42

micrub

7388 silver badges17 bronze badges

3 Comments

Míng Over a year ago

"npm install underscore" first

Eliran Malka Over a year ago

npm install -g underscore, you mean :)

Sam Berry Over a year ago

Why you shouldn't npm install -g

Mark Ursino · Accepted Answer · 2012-03-01 15:56:50Z

13

The name _ used by the node.js REPL to hold the previous input. Choose another name.

edited Mar 1, 2012 at 15:56

Mark Ursino

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answered Mar 1, 2012 at 13:04

dkiyatkin

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1 Comment

Kaushik Thirthappa Over a year ago

double underscore is better than _und i feel :)

Code Whisperer · Accepted Answer · 2015-09-06 18:04:21Z

-2

Note: The following only works for the next line of code, and only due to a coincidence.

With Lodash,

require('lodash');
_.isArray([]); // true

No var _ = require('lodash') since Lodash mysteriously sets this value globally when required.

edited Sep 6, 2015 at 18:04

answered Jul 4, 2015 at 22:30

Code Whisperer

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1 Comment

user578895 Over a year ago

No, this won't work with lodash or anything else. It works in your example because, as stated above, node sets the result of the last statement to _. The result of your last statement was the lodash lib. So _.isArray([]) will work on the next line, but never again.

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