Learn To Program JavaScript (in ten easy steps)

Just about every real-world program uses variables to store and reuse bits of data. Here I explain how to declare and use variables in JavaScript.

Here we’ll find out how JavaScript can get user input from a web page and assign that input to a variable in order to interact with the user. 

Functions are named subroutines. In this lesson, I explain how to write functions that can call one another and which may, optionally, return values to the code that called them.

Values can be passed into functions by sending one or more arguments that match the parameters declared in the function header. This video explains this.

‘Scope’ describes the visibility of items such as variables within your program. Here I explain the difference between local and global scope in JavaScript.

You will use strings all the time in your JavaScript code. Here we look at how  to use strings to display text and write HTML and how to embed special characters in strings.

String objects come with lots of built-in methods that can do everything from changing the case of a string to replacing part of a string. Here I look at a few string methods and find out a simple way of hiding your email address from Spam-gathering programs.

You will often need to perform conditional tests in your programs and take different actions according to whether or not the tests evaluate to true. Here I explain how to do ‘if’ and ‘else’ tests and how to do multiple tests using ‘case’ statements.

JavaScript provides a number of operators that can be used when testing values. Here I explain how these can be used and why some operators are stricter than others.

Learn how to use the add, subtract, multiply, divide and modulus operators to perform calculations or even create an interactive calculator on a web page.

What is the result of this calculation? 

10 * 5 - 2 / 3 

Is it 16? 10? Or some complicated floating-point number? In this lesson I show how the ‘precedence’ of mathematical operators affect the result of calculations and I explain a way of simplifying this.

Let’s assume that you ask a user to enter a number and they enter the text “fifty”. That’s a string, not a number and you obviously can’t do a calculation with it! So how to you deal with this kind of problem? One way is to use something called NaN. 

You want to write some code that executes only when both A and B are true or when either X or Y is true. You need to use the logical ‘and’ (&&) and ‘or’ (||) operators. This video explains how these work.