What Is Underscore?

Underscore.js is a JavaScript library supporting functional programming.

Getting Underscore

The Underscore website has the latest version of the library.

Using Underscore

_.times(4, function() {console.log("Major")});

// (console) Major
// (console) Major
// (console) Major
// (console) Major

var underscore = _.noConflict();

underscore.times(4, function() {console.log("Major")});

// (console) Major
// (console) Major
// (console) Major
// (console) Major

The Source Code for Functional JavaScript

Lemonad library and the official underscore-contrib library

Running the Code in This Book

The source code for Functional JavaScript is available on GitHub.

Notational Conventions

Avoid assigning variables more than once.
Do not use eval.
Do not modify core objects like Array and Function.
Favor functions over methods.
If a function is defined at the start of a project, then it should work in subsequent stages as well.
Functions of zero parameters are used to denote that the arguments don't matter.
In some examples, ... is used to denote that the surrounding code segments are being ignored.
Text like inst#method denotes a reference to an instance method.
I tend to restrict if/else statements to a single line per branch, so I prefer to avoid using curly brackets to wrap the blocks. This saves precious vertical space.
I like to use semicolons.

Whom Functional JavaScript Is Written For

Anyone looking to learn more about functional programming.

A Roadmap for Functional JavaScript

Chapter 1, Introducing Functional JavaScript
Chapter 2, First-Class Functions and Applicative Programming
Chapter 3, Variable Scope and Closures
Chapter 4, Higher-Order Functions
Chapter 5, Function-Building Functions
Chapter 6, Recursion
Chapter 7, Purity, Immutability, and Policies for Change
Chapter 8, Flow-Based Programming
Chapter 9, Programming Without Class

Conventions Used in This Book

Using Code Examples

......

Preface