JavaScript building blocks

In this module, we continue our coverage of all JavaScript's key fundamental features, turning our attention to commonly-encountered types of code blocks such as conditional statements, loops, functions, and events. You've seen this stuff already in the course, but only in passing — here we'll discuss it all explicitly.


Before starting this module, you should have some familiarity with the basics of HTML and CSS, and you should have also worked through our previous module, JavaScript first steps.

Note: If you are working on a computer/tablet/other device where you don't have the ability to create your own files, you could try out (most of) the code examples in an online coding program such as JSBin or Glitch.


Making decisions in your code — conditionals

In any programming language, code needs to make decisions and carry out actions accordingly depending on different inputs. For example, in a game, if the player's number of lives is 0, then it's game over. In a weather app, if it is being looked at in the morning, show a sunrise graphic; show stars and a moon if it is night. In this article we'll explore how conditional structures work in JavaScript.

Looping code

Sometimes you need a task done more than once in a row. For example, looking through a list of names. In programming, loops perform this job very well. Here we will look at loop structures in JavaScript.

Functions — reusable blocks of code

Another essential concept in coding is functions. Functions allow you to store a piece of code that does a single task inside a defined block, and then call that code whenever you need it using a single short command — rather than having to type out the same code multiple times. In this article we'll explore fundamental concepts behind functions such as basic syntax, how to invoke and define functions, scope, and parameters.

Build your own function

With most of the essential theory dealt with previously, this article provides a practical experience. Here you'll get some practice with building up your own custom function. Along the way, we'll also explain some further useful details of dealing with functions.

Function return values

The last essential concept you must know about a function is return values. Some functions don't return a significant value after completion, but others do. It's important to understand what their values are, how to make use of them in your code, and how to make your own custom functions return useful values.

Introduction to events

Events are actions or occurrences that happen in the system you are programming, which the system tells you about so you can respond to them in some way if desired. For example if the user clicks a button on a webpage, you might want to respond to that action by displaying an information box. In this article we will discuss some important concepts surrounding events, and look at how they work in browsers.

Event bubbling

This guide introduces the concepts of event bubbling, event capture, and event delegation, which are all about what happens when you add a listener to an element that contains another element, and an event then happens to the contained element.


The following assessment will test your understanding of the JavaScript basics covered in the guides above.

Now that we've looked at the fundamental building blocks of JavaScript, we'll test your knowledge of loops, functions, conditionals and events by building a fairly common item you'll see on a lot of websites — a JavaScript-powered image gallery.

See also

Learn JavaScript

An excellent resource for aspiring web developers — Learn JavaScript in an interactive environment, with short lessons and interactive tests, guided by automated assessment. The first 40 lessons are free, and the complete course is available for a small one-time payment.