Variables & Constants in JavaScript (OCR A Level Computer Science): Revision Note

Variables & Constants in JavaScript

What are variables and constants?

• Variables and constants are used to store a single item of data in a program

• This can be accessed through the identifier

• Variables can be changed during program execution while constants remain the same

Declaring variables & constants

• Variables are declared using a data type, a name and a value (optional)

• Constants are declared using the 'const' keyword, a name and a value

• In all programming languages, variable names should follow certain rules, such as:

  • Starting with a letter

  • Not containing spaces

  • Can contain letters, numbers, _ or $

  • Not using reserved words (like if, while, for etc.)

• Examples of data types include integer, float, boolean, and string

Examples in pseudocode:

Declare a variable called 'score' with a value of 10

score = 10

Declare a constant called 'PI' with a value of 3.14

const PI = 3.14

Examples in JavaScript:

let score = 10;

const PI = 3.14;