let-var-const

by

Let vs Var

				
					let question = () => {
  {
    let firstname = "anurag";
    var surname = "nayak";
  }

  console.log(firstname);
  console.log(surname);
};

question();

index.js:918 Uncaught ReferenceError: firstname is not defined
    at question (index.js:918:15)
    at index.js:922:1


				
			
				
					

let question1 = () => {
  {
    (function () {
      let firstname = "anurag";
      var surname = "nayak";
    });
  }
  console.log(surname);
  console.log(firstname);
};

question1();

Output
index.js:931 Uncaught ReferenceError: surname is not defined
    at question1 (index.js:931:15)
    at index.js:935:1

Guess the output -error ?

				
					const arr = [1, 2, 3];
arr.push(4);
console.log(arr);

output- [1,2,3,4]
				
			
				
					const arr = [1, 2, 3];
arr =[1,2,3,4];
console.log(arr);

//output- error

Guess the output -error ?

				
					const guessOutput = () => {
  console.log(employeeName);
  console.log(employeeId);

  var employeeName = "Anurag Nayak";
  let employeeId = "123";
};

guessOutput();

Uncaught ReferenceError: Cannot access 'employeeId' before initialization
    at guessOutput (index.js:1059:15)
    at index.js:1065:1

Guess the output

				
					let x = 1;
const guessOutput = () => {
  let x = 4;
  const inner = () => {
    x++;
    var x = 10;
    console.log(x);
  };
  inner();
};
guessOutput();

//Guess the output
//output should be 10...rest all x are distractions
//Its related to closure

let vs var - Random question

				
					for (let i = 0; i < 9; i++) {}
console.log(i); //Uncaught ReferenceError: i is not defined

for (var i = 0; i < 9; i++) {}
console.log(i); //9

var let const - redeclarable/updatable

				
					//****************var************************

var test = "test";
var test = "test changed";
console.log(test);
output:- test changed

//****************let************************

let test = "test";
//below redeclaration is not allowed as let is already declared
let test = "can I redeclare ??";

Guess the output

				
					let question = () => {
  return
  {
    name: "anurag";
  }
};

console.log(question());

output:-undefined
				
			
				
					let question = () => {
  return {
    name: "anurag"
  };
};

console.log(question());

output:-
{name: 'anurag'}

let vs var - Random question

				
					//This is allowed as var can be re-declared...
const question1 = () => {
  var x = "I am x";
  if (true) {
    var x = "I am getting modified...";
  }
};
question1();

//you cannot do this...as let variable cant be re-declared...
const question2 = () => {
  let x = "I am x";
  if (true) {
    var x = "I am getting modified...";
  }
};

let vs var - Random question

				
					{
  let x = "Can I be accessed outside this block ??";
}
//Uncaught ReferenceError: x is not defined
//console.log(x);

{
  var x = "Seems I can be accessed outside this block....";
}
//Seems I can be accessed outside this block....
console.log(x);

Leave a Comment