Functions Functions are one of the fundamental building blocks in JavaScript. A function in JavaScript is similar to a procedure—a set of statements that performs a task or calculates a value, but for a procedure to qualify as a function, it should take some input and return an output where there is some obvious relationship between the input and the output. To use a function, you must define it somewhere in the scope from which you wish to call it. Quite often we need to perform a similar action in many places of the script. For example, we need to show a nice-looking message when a visitor logs in, logs out and maybe somewhere else. Functions are the main “building blocks” of the program. They allow the code to be called many times without repetition. Defining functions Function declarations A function definition (also called a function declaration , or function statement ) consists of the function keyword, followed by: The name of the functi...