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JavaScript The Module Pattern in JavaScript

Posted by Olivia Posch
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Olivia Posch
Front End Web Development Techdegree Graduate 19,720 Points

I don't undertsand what's wrong with it: Error: Uncaught ReferenceError: _ is not defined

!function(underscore) { underscore.someawesomemethod = "yay!!!"; console.log(underscore.VERSION); }(_);

2 Answers

Neil McPartlin
Neil McPartlin
14,662 Points
Neil McPartlin
Neil McPartlin
14,662 Points

Hi Olivia. All becomes clear once you realise that 'underscore' is actually a JavaScript library (http://underscorejs.org/) which you may or may not have available in your browser (session). The code you have written is correct. In fact you are reading this post in a tab of your browser which may already have 'underscore' installed. For me, in my Chrome browser, if I literally select F12 (important, you must stay on this same tab), to open the devtools Javascript console, then copy/paste in your code, I get back...

1.8.3

true

In contrast, this currently does not work when using Treehouse Workspaces. Maybe something has changed since this video was shot in 2015. I don't know the contents of the teacher's index.html, but if you use this index.html file, it should help.

index.html

<!doctype html>
<html>
    <head>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.8.3/underscore.js"></script>
    </head>
    <body>
    <script src="pattern.js"></script>
    </body>
</html>
Olivia Posch
.a{fill-rule:evenodd;}techdegree seal-36
Olivia Posch
Front End Web Development Techdegree Graduate 19,720 Points

thank you very much neil! now is everything clear .

Lee Cockcroft
Lee Cockcroft
10,278 Points
Lee Cockcroft
Lee Cockcroft
10,278 Points

You have an underscore in between the brackets "(_)"

!function(underscore) { underscore= "yay!!!"; console.log(underscore); }();

I get 'yay' in the console log running this.

Olivia Posch
.a{fill-rule:evenodd;}techdegree seal-36
Olivia Posch
Front End Web Development Techdegree Graduate 19,720 Points

thank you Lee for the answer but in exemplo from the video 'Pattern' it is:
!function(underscore) { underscore.someawesomemethod = "yay!!!"; console.log(underscore.VERSION); }(_);

or like this:

!function(){ underscore.someawesomemethod = "yay!!!"; console.log(underscore.VERSION); }();

but i think it is a old version ...