This is a borderline question, but I figured it was worth asking. Is the below the most concise way to check if underscore.js is loaded, and are there any draw-backs to this approach.

typeof _  == "function" ? console.log('yes') : console.log('no');

Honestly my "real" question is as follows. Basically this is a plugin that is going to be used on alot of front-end frameworks. Some will have underscore and some will not. In order to make it universal and to use the methods provided by underscore I want to check for underscore and provide fallback if not present while electing to use it when I can.

Is this bad practice and should I not even bother with using underscore when it is present?

NOTE: Unfortunately lodash.js is not an option because I foolishly shimmed underscore.js into the require config, and people don't seem to understand the necessity of AMD patible modules.

This is a borderline question, but I figured it was worth asking. Is the below the most concise way to check if underscore.js is loaded, and are there any draw-backs to this approach.

typeof _  == "function" ? console.log('yes') : console.log('no');

Honestly my "real" question is as follows. Basically this is a plugin that is going to be used on alot of front-end frameworks. Some will have underscore and some will not. In order to make it universal and to use the methods provided by underscore I want to check for underscore and provide fallback if not present while electing to use it when I can.

Is this bad practice and should I not even bother with using underscore when it is present?

NOTE: Unfortunately lodash.js is not an option because I foolishly shimmed underscore.js into the require config, and people don't seem to understand the necessity of AMD patible modules.

• javascript

• Well, all the test tells you that _ is a function, not whether it is underscore.js or not. – Felix Kling Commented Oct 11, 2014 at 1:02
• 1 You shouldn't bother. Make underscore a dependency of your project and use it, or don't, and don't. You can't have it both ways; there is literally no benefit to doing so. – user229044 ♦ Commented Oct 11, 2014 at 1:30
• Underscore minified is tiny. It costs you nothing to just leave it loaded. – dgo Commented Oct 11, 2014 at 1:43
• The environments will vary, and there is a major memory improvement when it's methods are used pared to standard JavaScript as I am dealing with very large arrays (millions) with nested objects. – MattSizzle Commented Oct 11, 2014 at 2:05
• @meagar I'm not sure you are understanding. It's not a project, it's a plugin for other projects which may or may not use things like poser. There is def a benefit to checking. Like when one plugin wants to load underscore even though another plugin may have already loaded it. Same thing goes for Fontawesome, Bootstrap, etc. IMO you should always check, for the sake of plugin sanity. – dhaupin Commented May 4, 2016 at 15:48

2 Answers 2

Given that Underscore is exported as a function, it's correct to say that performing a type check is the most concise way of checking if Underscore is available in memory. If I get it right - for some weird reason, I gotta say -, you want to implement a feature checking so contexts that doesn't have specific method implementations will gracefully degrade.

You could simply check for Underscore and for the feature you want. Since each feature is a property of Underscore you can check if it's defined or not through type checking as well:

if(typeof _ === 'function') {
  if(typeof _.reduce !== 'undefined') {
    // fallback goes here
  }
}

Just keep in mind that depending on the feature you're trying to fallback you might lose Underscore's chaining capabilities. I would double check that.

I also wanted to test if Lodash was loaded and this piece of code works both for Lodash and Underscore:

(function () {
    if (_.VERSION) {
    console.log('underscore loaded');
  }
})();

https://jsfiddle/2x0g8xyt/