Question

What is the difference between var and let in JavaScript

Answer 1

// one i: start as 'abc', finish as 5

var i = 'abc'; 
for (var i = 0; i < 5; i++) {
    console.log("i = ", i); 
}

console.log(i);

// two j: first j is 'abc', second j is 0 to 5 in for block  

let j = 'abc'; 
for (let j = 0; j < 5; j++) {
    console.log("j = ", j); 
}

console.log(j);



     
/*
run:
   
i =  0
i =  1
i =  2
i =  3
i =  4
5
j =  0
j =  1
j =  2
j =  3
j =  4
abc
 
*/

 

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Answer 2

var a = 5;
var a = 30;
console.log(a); // 30


let b = 5;
let b = 30; // SyntaxError: Identifier 'b' has already been declared

console.log(b);



     
/*
run:
   
let b = 30; // SyntaxError: Identifier 'b' has already been declared
 
*/

 

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Answer 3

var a = 5;
if (true)
    var a = 30; // Same variable: a
console.log(a); // 30


let b = 5;
if (true)
    let b = 30; // SyntaxError: Identifier 'b' has already been declared

console.log(b);



     
/*
run:
   
let b = 30; // SyntaxError: Identifier 'b' has already been declared
 
*/

 

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Answer 4

var a = 7;
if (true) {
    var a = 30; // Same variable: a
}
console.log(a); // 30


let b = 7;
if (true) {
    let b = 30; 
}

console.log(b);



     
/*
run:
   
30
7
 
*/

 

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