JavaScript Concept

One of the first and most important concepts you encounter in JavaScript is variables

JavaScript provides three main ways to declare variables:

1. var,
2. let, and
3. const

While they may look similar, they behave very differently.

Variable

A variable is like a container that holds a value. You give it a name so you can reference or update that value later in your code.

Example:
let age = 16;

Here, age is assigned to a value of 16.

1. var – The Old Way: var is the older method of declaring variables in JavaScript.

Key features of var:

• Function scoped
• Can be redeclared
• Can be updated

Example:
Redeclaration
var fruit = "orange"; // declearation
var fruit = "apple"; //redeclearation
console.log(fruit); // apple

Making update
var fruit = "orange";
fruit = "apple"; // update
console.log(fruit); // apple

Redeclaring a variable may overwrite values unexpectedly, making bugs harder to track.

1. let – This was introduced to fix many of the problems caused by var.

Key features of let:

• Block scoped can be updated
• redeclared.

Example:
let age = 16; // declaration
age = 17; // updating (allowed)
console.log(age); // 17

// Redeclaring in the same scope will cause an error:
let age = 16;
if (true) {
let age = 18; // allowed, block-scoped
}

1. const – const is used for Fixed Values. const is used for values that should never change.

Key features of const:

• Block scoped,
• Cannot be updated and
• Cannot be redeclared.
• It Must be initialized immediately

Example:

const country = "Nigeria";

Using the correct variable type helps:

• Prevent bugs
• Make your code more readable
• Improve maintainability

Best Practices for Declaring Variables in JavaScript:

• Use const by default — for values that should not change.
• Use let only when you need to update or reassign a variable.
• Avoid var in modern JavaScript to prevent unexpected redeclarations and scope issues.