Written by Gary Kenneally
on July 21, 2013

Functional javascript using underscore

Why?

A little while ago I picked up Functional Javascript by Michael Fogus. I’m only part way through it and to be honest I should probably have waited until I finished it before starting this post but…

There is a central theme to this book which intrigued me, indeed its one of the main tenets of functional programming. It can be summed up in this quote:

“It is better to have 100 functions operate on one data structure than 10 functions on 10 data structures.” - Alan Perlis

This is very different concept to what is normally seen in large enterprise level projects and applications. I have to say that I have spent a large amount of time writing code to map one model to another and back again. Its not fun. This functional stuff might be on to something.

What?

Well Michaels book uses the underscore library for all of his examples and its a really powerful tool. I have started using it here and there on smaller projects and the more I use it the more I like it.

How?

Project Euler is probably the go-to set of problems when developers try to learn a new language or framework. I don’t see why I should be any different. I have started a small project to play around with this and you can see it over on github.

Problem 1

If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23. Find the sum of all the multiples of 3 or 5 below 1000.

Can be solved with a few lines of code like the following:

    return _.reduce(_.range(0,1000), function(memo, number){  
    		if( number%3===0 || number%5==0) return memo+number;  
    		return memo;}  
    	);

Testing

Unit testing javascript has come a long way in the last few years and I have added a simple QUnit test runner to the repository.

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