Book Image

Mastering JavaScript

By : Ved Antani
Book Image

Mastering JavaScript

By: Ved Antani

Overview of this book

JavaScript is a high-level, dynamic, untyped, lightweight, and interpreted programming language. Along with HTML and CSS, it is one of the three essential technologies of World Wide Web content production, and is an open source and cross-platform technology. The majority of websites employ JavaScript, and it is well supported by all modern web browsers without plugins. However, the JavaScript landscape has changed dramatically in recent years, and you need to adapt to the new world of JavaScript that people now expect. Mastering modern JavaScript techniques and the toolchain are essential to develop web-scale applications. Mastering JavaScript will be your companion as you master JavaScript and build innovative web applications. To begin with, you will get familiarized with the language constructs and how to make code easy to organize. You will gain a concrete understanding of variable scoping, loops, and best practices on using types and data structures, as well as the coding style and recommended code organization patterns in JavaScript. The book will also teach you how to use arrays and objects as data structures. You will graduate from intermediate-level skills to advanced techniques as you come to understand crucial language concepts and design principles. You will learn about modern libraries and tools so you can write better code. By the end of the book, you will understand how reactive JavaScript is going to be the new paradigm.
Table of Contents (16 chapters)
Mastering JavaScript
Credits
About the Author
About the Reviewer
www.PacktPub.com
Preface
Index

Function declarations versus function expressions


We saw two ways by which functions are defined. Though they both serve identical purposes, there is a difference between these two types of declarations. Check the following example:

//Function expression
functionOne();
//Error
//"TypeError: functionOne is not a function

var functionOne = function() {
  console.log("functionOne");
};
//Function declaration
functionTwo();
//No error
//Prints - functionTwo

function functionTwo() {
  console.log("functionTwo");
}

A function declaration is processed when execution enters the context in which it appears before any step-by-step code is executed. The function that it creates is given a proper name (functionTwo() in the preceding example) and this name is put in the scope in which the declaration appears. As it's processed before any step-by-step code in the same context, calling functionTwo() before defining it works without an error.

However, functionOne() is an anonymous function expression, evaluated...