JavaScript Variables

There are 3 ways to declare a JavaScript variable:

   • Using var

   • Using let

   • Using const


Variables

Variables are containers for storing data (values).

In this example, xy, and z, are variables, declared with the var keyword:

Creating a variable in JavaScript is called "declaring" a variable. You declare a JavaScript variable with the var keyword: var carName;

EXAMPLE ❯


JavaScript Identifiers

All JavaScript variables must be identified with unique names.

These unique names are called identifiers.

Identifiers can be short names (like x and y) or more descriptive names (age, sum, totalVolume).

The general rules for constructing names for variables (unique identifiers) are:

  • Names can contain letters, digits, underscores, and dollar signs.

  • Names must begin with a letter

  • Names can also begin with $ and _ (but we will not use it in this tutorial)

  • Names are case sensitive (y and Y are different variables)

  • Reserved words (like JavaScript keywords) cannot be used as names


The Assignment Operator

In JavaScript, the equal sign (=) is an "assignment" operator, not an "equal to" operator.

Assignment operators are used to assigning value to a variable.

The left side operand of the assignment operator is a variable and right side operand of the assignment operator is a value. ... This operator is used to assign the value on the right to the variable on the left. 

Example:

x = x + 5


JavaScript Data Types

In programming, text values are called text strings.

JavaScript can handle many types of data, but for now, just think of numbers and strings.

Strings are written inside double or single quotes. Numbers are written without quotes.

If you put a number in quotes, it will be treated as a text string.

EXAMPLE ❯


Declaring (Creating) JavaScript Variables

Creating a variable in JavaScript is called "declaring" a variable.

You declare a JavaScript variable with the var keyword:

Example:

var carName;


After the declaration, the variable has no value (technically it has the value of undefined).

To assign a value to the variable, use the equal sign:

carName = "Volvo";


You can also assign a value to the variable when you declare it:

EXAMPLE ❯