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;

Examiner Tips and Tricks

• You might see code that declares variables like this

var variableName = value;

• This is bad practice as it utilises global variables but was used until 2015 when let was added to JavaScript