JavaScript Using Variables

JavaScript Using Variables

Variables in JavaScript are basically named buckets of data, a way of creating a reference to that data—regardless of whether the data is a string, number, boolean, array, or other object—so that you can access the same data again and again. More importantly, you can use variables to persist data from one process to another. For instance, your JavaScript application can store the value of a form element in a variable, and manipulate that value without having to actually manipulate the form element itself.

As with algebra, JavaScript variables can be used to hold values (x=5) or expressions (z=x+y).

Variable can have short names (like x and y) or more descriptive names (age, sum, totalvolume).

Variable names must begin with a letter

Variable names can also begin with $ and _ (but we will not use it)

Variable names are case sensitive (y and Y are different variables)

Declaring (Creating) JavaScript Variables

Creating a variable in JavaScript is most often referred to as "declaring" a variable.

You declare JavaScript variables with the var keyword:

javascriptvariables

Variables in JavaScript behave the same as variables in most popular programming languages (C, C++, etc) do, but in JavaScript you don't have to declare variables before you use them. If you don't know what declaring is, don't worry about it. It isn't important!

avariable example

When using a variable for the first time it is not necessary to use "var" before the variable name, but it is a good programming practice to make it crystal clear when a variable is being used for the first time in the program. Here we are showing how the same variable can take on different values throughout a script.

IdentifyingVariables

JavaScript variables have an identifier, scope, and a specific data type. Because the language is loosely typed, the rest, as they say, is subject to change without notice.

Variables in JavaScript are much like those in any other language; you use them to hold values in such a way that the values can be explicitly accessed in different places in the code. Each has an identifier that is unique to the scope of use (more on this later), consisting of any combination of letters, digits, underscores, and dollar signs. An identifier doesn’t have a required format, other than it must begin with a character, dollar sign, or underscore: