In Javascript, variables are used to store data.

In the example, variables a, b, and c are defined and assigned values.

var a = 5;
var b = 6;
var c = a + b;

Defined variables:

  • The value of a variable is 5
  • The value of variable b is 6
  • The value of variable c becomes 11.

Variable definition

All Javascript variable names must be unique.

Javascript variable names are called identifiers.

Identifiers can be short like a and b, or more descriptive like birthDate, firstName, age

Variable declaration rules

  • Variable names can contain letters, numbers, underscores, and dollar signs.
  • Variable names can begin with a letter, underscore, or dollar sign.
  • Variable names are CASE-sensitive. (a and A are different variables)
  • No spaces between variable names.
  • Javascript keywords cannot be used as variable names. (var, debugger, if, while, etc…)

Value assignment

The equal (=) operator is used to assign a value to a variable in Javascript.

var a = 5;

Variable types

Javascript variables can take numeric values like 100 or text values like Baransel Arslan.

Strings are written in single or double quotes, while numeric values are written without quotation marks.

If numeric values are enclosed in quotes, Javascript will define the variable as a string.

var pi = 3.14;
var name = "Baransel Arslan";
var age = 21;

Creating a variable

Javascript variable creation is called variable declaration.

The var, const, let keyword is used to create variables with Javascript.

We will learn about const and let keywords in the later post.

var name;

After creating a variable, the variable has no value. (The variable value is defined as undefined.)

The equal (=) operator is used to assign a value to a variable.

name = "Baransel Arslan";

We can also assign a value to a variable while creating a variable.

var name = "Baransel Arslan";

Variable arithmetic

We can use arithmetic operators on Javascript variables.

var a = 5 + 2 + 3;

When we use arithmetic operators on string values, it will act as a concatenation operator.

var a = "Baransel " + "Arslan";

When numbers are written in quotes, the Javascript string concatenation operator will be performed.

var a = "5" + 2 + 3;