Variables & Data types in JavaScript

Variables & Data types in JavaScript

A variable provides us with named storage that our programs can manipulate. Variables are used to store information to be referenced and manipulated in a computer program.

In programming, a variable is a value that can change, depending on conditions or on information passed to the program.

Why do we need variables? Answer: To store data

Some example of data types in JavaSript is:

  • String

  • The Number type (includes Integers, floating-point numbers, exponential notation, and so on.)

  • Booleans (true & false)

  • Undefined type

  • Null data type

  • Object data type.

  • Arrays

  • The typeof Operator

    Naming conventions for variables in JavaScript

The rules for creating an identifier in JavaScript is:

  • JavaScript variables must be identified with unique names.

  • Names must begin with a letter

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

  • The name of the identifier should not be any pre-defined keyword.

  • The first character must a letter, an underscore(_), or a dollar sign ($).

Subsequent characters may be any letter, digit, underscore, or any character. Variables are Case sensitive. (y and Y are different variables)

Using let and const

Before 2015, using the var keyword was the only way to declare a JavaScript variable.

But now, JavaScript ES6 (ES6 - ECMAScript 2015) allows the use of the const keyword to define a variable that cannot be reassigned, and the let keyword to define a variable with restricted scope.

Safari 10 and Edge 14 were the first browsers to fully support ES6.

The Assignment Operator

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

let name = 'Mike'

The "equal to" operator is written like == in JavaScript.

Declaring (Creating) JavaScript Variables

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

You declare a JavaScript variable with the let or const keyword:

let 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 = 'Tesla'

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

const age = 18

Remember that JavaScript identifiers (names) must begin with:

  • A letter (A-Z or a-z)
  • A dollar sign ($)
  • Or an underscore (_)

Since JavaScript treats a dollar sign as a letter, identifiers containing $ are valid variable names.