Basic Javascript Knowledge: When to use var, let or const?

In JavaScript, variables are essential for storing data. The keywords var, let, and const provide different ways to declare these variables.

var

• Scope: Function scope.
• Hoisting: Variables are hoisted.
• Re-assignment: Allowed.
• Re-declaration: Allowed.

 function testVar() { var x = 1; if (true) { var x = 2; // same variable! console.log(x); // 2 } console.log(x); // 2 } testVar(); 

let

• Scope: Block scope.
• Hoisting: Hoisted but not initialized.
• Re-assignment: Allowed.
• Re-declaration: Not allowed.

 function testLet() { let y = 1; console.log(y); // 1 if (true) { let y = 2; // different variable console.log(y); // 2 } y = 5 console.log(y); // 5 } testLet(); 

const

• Scope: Block scope.
• Hoisting: Hoisted but not initialized.
• Re-assignment: Not allowed.
• Re-declaration: Not allowed.
• Initialization: Required during declaration.

 function testConst() { const z = 1; // z = 2; // Error: Uncomment this see error console.log(z); } testConst(); 

Exercise: Try This To Practise Using Variables

1. Var Scope: Use var in a loop, then access it outside.
2. Let Block Scope: Try let in a loop and access it outside the block.
3. Const Immutability: Attempt re-assigning a const variable.

Good luck!