Top 50 Most Asked JavaScript Logical Output Interview Q&A

Hey Rowdy Coders, In my recent job switch, I have been interviewed at many companies. In this article, I will be sharing all the Top 50 Most Asked JavaScript output-based Interview Questions and Answers.

JavaScript Interview Questions

⭐️. Guess the output of the following code?

console.log(5 > '15' < 5);
console.log(7 < '15' < 7);
console.log(7 < '85' > 5);

false, false, true true, false, true false, false, false true, true, false

⭐️. Guess the output of the following code?

console.log(1);

setTimeout(() => {
  console.log(2);
}, 1000);
          
setTimeout(() => {
  console.log(3);
}, 0);
          
console.log(4);

1, 2, 3, 4 1, 4, 3, 2 1, 3, 4, 2 3, 1, 4, 2

⭐️. Guess the output of the following code?

console.log(1);

setTimeout(() => {
  console.log(2);
}, 1000);

setTimeout(() => {
  console.log(3);
}, 0);

Promise.resolve(1).then(function resolve() {
  setTimeout(() => {
    console.log(4);
  }, 0);
});

console.log(5);

1, 2, 3, 4, 5 1, 5, 3, 4, 2 1, 3, 4, 2, 5 1, 4, 3, 2, 5

⭐️. Guess the output of the following code?

for (var i = 0; i < 4; i++) {
  console.log(i);
}

for (let i = 0; i < 4; i++) {
  console.log(i);
}

0, 1, 2, 3, 0, 1, 2, 3 0, 1, 2, 3, 4, 5, 6, 7 4, 4, 4, 4, 0, 1, 2, 3 undefined, undefined, undefined, undefined, 0, 1, 2, 3

⭐️. Guess the output of the following code?

for (var i = 0; i < 4; i++) {
    setTimeout(() => {
      console.log(i);
    }, 500);
}

for (let i = 0; i < 4; i++) {
    setTimeout(() => {
      console.log(i);
    }, 7000);
}

for (var i = 0; i < 4; i++) {
    (function (i) {
      setTimeout(function () {
        console.log(i);
      }, 14000);
    })(i);
}

0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 2 4, 4, 4, 4, 0, 1, 2, 3, 0, 1, 2, 3

⭐️. Guess the output of the following code?

console.log(["a"] + ["b"]);

console.log([] + []);

console.log(![]);

console.log(![] + []);

ab, '' , false, false a, b, true, false ab, empty, false, emptyfalse a + b, [], true, false + []

⭐️. Guess the output of the following code?

console.log(3 < 4 < 5);

console.log(3 > 4 > 5);

console.log(3 > 4 > -1);

true, true, false false, true, true true, false, true true, false, false

⭐️. Guess the output of the following code?

const x1 = new Promise((res, req) => {
  setTimeout(res, 500, "one");
});

const x2 = new Promise((res, req) => {
  setTimeout(res, 100, "two");
});

Promise.all([x1, x2]).then((res) => {
  console.log(res);
});

Promise.race([x1, x2]).then((res) => {
  console.log(res);
});

['one', 'two'], two two, ['one', 'two'] one, two ['one'], two

⭐️. Guess the output of the following code?

const a = {};
const b = { key: "b" };
const c = { key: "c" };

a[b] = 143;
a[c] = 286;

console.log(a[b]);

console.log(b.toString());

286, [object Object] 143, [object Object] undefined, [object Object] 286, { key: 'b' }

⭐️. Guess the output of the following code?

const h1 = { h: "Thor", i: "IM" };
const h2 = { h: "Thor", i: "IM" };
const h3 = h2;
console.log(h1 == h2);
console.log(h1 === h2);
console.log(h2 === h3);

true, true, true false, true, false true, false, true false, false, true

⭐️. Guess the output of the following code?

const array1 = [1, 2, 3];
const array2 = [1, 2, 3];
const array3 = array2;
console.log(array1 === array2);
console.log(array2 === array3);

const User = function (name) {
this.name = name;
};
const user1 = new User("Rowdy");
const user2 = new User("Rowdy");
console.log(user1 == user2);

false, true, true false, true, false true, true, false true, true, true

⭐️. Guess the output of the following code?

console.log((1 && 2) || 0 || 3);

console.log(null && undefined);

console.log(0 || (1 && 2) || 3);

console.log(null || (2 && 3) || 4);

2, undefined, 2, 3 2, null, 2, 3 1, undefined, 1, 3 2, null, 2, 2

⭐️. Guess the output of the following code?

console.log('goog' > 'bad');

console.log('Like' < 'like');

console.log('Subscribe' > 'Subg');

console.log('SubScribe' > 'Subg');

false, true, true, false true, false, false, true true, false, true, false true, true, true, false

⭐️. Guess the output of the following code?

console.log("9" > "11");

console.log("9" > 11);

console.log("" > -1);

console.log("Rowdy" > 1);

true, false, false, true false, false, false, true true, false, true, false true, true, false, false

⭐️. Guess the output of the following code?

console.log(Math.round(5.51));
console.log(Math.round(-5.51));

console.log(Math.floor(5.51));
console.log(Math.floor(-5.51));

console.log(Math.ceil(5.51));
console.log(Math.ceil(-5.51));

console.log(Math.abs(-5.51));
console.log(Math.abs(5.51));

6, -5, 5, -6, 6, -5, 5.51, 5.51 6, -6, 6, -6, 6, -5, 5.51, 5.51 6, -6, 5, -6, 6, -5, 5.51, 5.51 6, -6, 5, -5, 6, -5, 5.51, 5.51

⭐️. Guess the output of the following code?

function Name() {
return
{
  mes: "JavaScript";
}
}
console.log(Name());

function caName() {
return {
  mes: "Rowdy Coder",
};
}
console.log(caName());

undefined, {mes: 'Rowdy Coder'} {mes: 'JavaScript'}, {mes: 'Rowdy Coder'} undefined, undefined {mes: 'JavaScript'}, undefined

⭐️. Guess the output of the following code?

var array = [1, 2, 3, 4, 5];
console.log(array.length);

array.length = 3;

console.log(array.length);
console.log(array);

delete array[0];

console.log(array);
console.log(array[0]);
console.log(array.length);

5, 3, [1, 2, 3], [1, 2, 3], 1, 3 5, 5, [1, 2, 3, 4, 5], [empty × 1, 2, 3], 1, 5 5, 3, [1, 2, 3, 4, 5], [empty × 1, 2, 3], undefined, 3 5, 3, [1, 2, 3], [empty × 1, 2, 3], undefined, 3

⭐️. Guess the output of the following code?

const arr = [1, 2, 3];
const str = "1,2,3";

console.log(arr == str);

true false

⭐️. Guess the output of the following code?

console.log(3 + 3 + "3" + 3 + 3);

console.log(1 + 2 + 3 + 4 + 5 + "6");

63333, 1536 33333, 156 63333, 156 3333, 1536

⭐️. Guess the output of the following code?

var arr1 = [
[1, 2],
[2, 4],
[4, 8],
];
var arr2 = [...arr1];

arr1[0][1] = "1";
arr1[0][0] = "0";
arr1[1] = 33;
arr1[0] = 22;
console.log(arr1);
console.log(arr2);

[ [ 0, 1 ], 33, 22 ], [ [ 0, 1 ], [ 2, 4 ], [ 4, 8 ] ] [ [ 22, 33 ], 4, 8 ], [ [ 0, 1 ], [ 2, 4 ], [ 4, 8 ] ] [ [ 0, 1 ], 33, 22 ], [ [ 1, 2 ], [ 2, 4 ], [ 4, 8 ] ] [ 22, 33, [ 4, 8 ] ], [ [ '0', '1' ], [ 2, 4 ], [ 4, 8 ] ]

⭐️. Guess the output of the following code?

var testArrowFunc = {
  name: "abc",
  foo: () => {
    console.log(this.name);
  },
};

var output = testArrowFunc.foo;
output();
testArrowFunc.foo();

var testFunc = {
  name: "abc",
  foo: function () {
    console.log(this.name);
  },
};

var output = testFunc.foo;
output();
testFunc.foo();

undefined, undefined, undefined, abc undefined, abc, undefined, abc undefined, undefined, abc, abc abc, undefined, undefined, abc

⭐️. Guess the output of the following code?

console.log(0.1 + 0.2 == 0.3) ;
console.log(0.3 + 0.6 == 0.9) ;

// Output in explanation!
console.log(0.1 + 0.2)  
console.log(0.3 + 0.6)

false, true true, true false, false true, false

⭐️. Guess the output of the following code?

console.log("first");

setTimeout(() => {
  console.log("second");
});

queueMicrotask(() => {
  console.log("third");
});

first, second, third first, third, second second, first, third third, first, second

⭐️. Guess the output of the following code?

console.log(num);
var num;
num = 6;
console.log(num);

numb = 6;
console.log(numb);
let numb;

undefined, 6, Error undefined, 6, undefined undefined, undefined, Error 6, 6, Error

⭐️. Guess the output of the following code?

function* myGenerator() {
    yield 1;
    yield 2;
    yield 3;
}

const gen = myGenerator();

console.log(gen.next());

{ value: 1, done: false } { value: 2, done: false } { value: 1, done: true } { value: 2, done: true }

⭐️. Guess the output of the following code?

console.log(6 + "7");

console.log(true + 5);

console.log(true + "5");

13, 6, true5 67, 6, 6true 13, true5, 6 67, 6, true5

⭐️. Guess the output of the following code?

function exm() {
    const name = "Rowdy Coders";
    function inner() {
      return name;
    }
    return inner;
}
const inner_func = exm();
console.log(inner_func);
console.log(inner_func());

[Function: inner], Rowdy Coders inner, Rowdy Coders [Function: inner], undefined [Function: inner], null

⭐️. Guess the output of the following code?

console.log("begins");

setTimeout(() => {
  console.log("setTimeout 1");
  Promise.resolve().then(() => {
    console.log("promise 1");
  });
}, 0);

new Promise(function (resolve, reject) {
  console.log("promise 2");
  setTimeout(function () {
    console.log("setTimeout 2");
    resolve("resolve 1");
  }, 0);
}).then((res) => {
  console.log("dot then 1");
  setTimeout(() => {
    console.log(res);
  }, 0);
});

begins, promise 2, setTimeout 1, setTimeout 2, promise 1, dot then 1, resolve 1 begins, promise 2, setTimeout 2, promise 1, setTimeout 1, dot then 1, resolve 1 begins, promise 2, setTimeout 1, promise 1, setTimeout 2, dot then 1, resolve 1 begins, promise 2, setTimeout 1, promise 1, setTimeout 2, resolve 1, dot then 1

⭐️. Guess the output of the following code?

async function async1() {
  console.log("async1 start");
  await async2();
  console.log("async1 end");
}

async function async2() {
  console.log("async2");
}

console.log("script start");

setTimeout(function () {
  console.log("setTimeout");
}, 0);

async1();

new Promise(function (resolve) {
  console.log("promise1");
  resolve();
}).then(function () {
  console.log("promise2");
});

console.log("script end");

script start, async1 start, async2, promise1, script end, promise2, async1 end, setTimeout script start, async1 start, promise1, script end, promise2, async2, async1 end, setTimeout script start, async1 start, async2, promise1, script end, async1 end, promise2, setTimeout script start, async1 start, async2, promise1, script end, setTimeout, promise2, async1 end

⭐️. Guess the output of the following code?

new Promise(function (resolve, reject) {
  setTimeout(function () {
    resolve("Promise");
  }, 1000);
}).then(function (result) {
  console.log(result);
});

setTimeout(callback, 2000);

// setTimeout()
setTimeout(function () {
  console.log("setTimeout()");
}, 2000);

// Callbacks
function callback() {
  console.log("Callback");
}

process.nextTick(function () {
  console.log("process.nextTick()");
});

process.nextTick(), Promise, setTimeout(), Callback process.nextTick(), Promise, Callback, setTimeout() setTimeout(), Promise, Callback, process.nextTick() Promise, process.nextTick(), setTimeout(), Callback

⭐️. Guess the output of the following code?

const obj = {
    name: "Billy",
    sing: function () {
      this.age = "20";
      console.log("a", this);
      var anotherFunction = function () {
        this.age = "30";
        console.log("b", this);
      };
      anotherFunction();
    },
};
obj.sing();

a { name: 'Billy', sing: [Function: sing], age: '20' }, b { age: '30' } a { name: 'Billy', sing: [Function], age: '20' }, b { name: 'Billy', sing: [Function], age: '30' } a { name: 'Billy', sing: [Function: sing], age: '20' }, b { name: 'Billy', age: '30' } a { name: 'Billy', sing: [Function: sing], age: '20' }, Window

⭐️. Guess the output of the following code?

const a = {
  count: 0,
};

const b = a;
b.count = a.count++;

console.log(b.count, a.count);

0, 1 1, 1 1, 0 0, 0

⭐️. Guess the output of the following code?

const a1 = {
  count: 0,
};

const b1 = a1;
b1.count = ++a1.count;

console.log(b1.count, a1.count);

0, 1 0, 0 1, 0 1, 1

⭐️. Guess the output of the following code?

const s = {
  hello: "sri",
  34: undefined,
  1: "HELLO",
  2: "SSS",
};
s["assign"] = "world";
s[-4] = "mee";

console.log(Object.keys(s));

['1', '2', '34', 'assign', '-4'] ['1', '2', '34', '-4', 'assign'] ['assign', '-4', '1', '2', '34'] ['hello', '34', '1', '2', 'assign', '-4']

⭐️. Guess the output of the following code?

(function (x) {
  console.log("First IIFE executed");

  return (function (y) {
    console.log("Nested IIFE executed", x);
})(2);
})(1);

First IIFE executed, Nested IIFE executed 2 First IIFE executed, Nested IIFE executed 1 Nested IIFE executed, First IIFE executed 1 First IIFE executed, Nested IIFE executed 1, 2

⭐️. Guess the output of the following code?

var obj = {
  name: "sri",
  age: 10,
}  

var obj1 = obj;

obj1.age = "20";

Object.freeze(obj);
obj1.age = "30";
console.log(obj.age);
console.log(obj1.age);

30, 30 20, 30 20, 20 10, 10

⭐️. Guess the output of the following code?

console.log('start');

setTimeout(()=>{
  console.log('mid');
}, 0);

for(let i=0;i<10000;i++){
  console.log('thread block');
}

console.log('end');

start, mid, end, thread block (repeated 10000 times) start, thread block (repeated 10000 times), end, mid start, end, thread block (repeated 10000 times), mid start, thread block (repeated 10000 times), mid, end

⭐️. Guess the output of the following code?

console.log(varA);
console.log(letB);

var varA = "Rowdy Coders";
let letB = 'Subscribe';

undefined, ReferenceError undefined, undefined ReferenceError, ReferenceError ReferenceError, undefined

⭐️. Guess the output of the following code?

let value = "Rowdy Coders"
value[1] = "A";

console.log(value);
console.log(value[0], value[1]);

Rowdy Coders, R A RAwdy Coders, R o Rowdy Coders, R o Rowdy Coders, R w

⭐️. Guess the output of the following code?

function tryCatchFinally(){
   try {
    console.log("try");
    return;
   } catch(e){
    console.log("error");
    return;
   } finally {
    console.log("finally");
    return;
  }
}
tryCatchFinally();

try, finally try, error, finally finally, try error, finally, try

⭐️. Guess the output of the following code?

let flag = true;
setTimeout(()=>{
  flag = false;
}, 1000)

while(flag){
  console.log("Does it execute?")
}

Infinite loop Does it execute? Executes for 1000ms Executes once

⭐️. Guess the output of the following code?

abc();

function abc(){
  console.log("1");
}

function abc(){
  console.log("2");
}

function abc(){
  console.log("3");
}

1 2 3 undefined

⭐️. Guess the output of the following code?

const person ={
  name: "Rowdy",
  age: 1,
  name: "Coders"
}
console.log(person);

{ name: 'Rowdy', age: 1 } { name: 'Coders', age: 1 } { name: 'Coders', age: 0 } { name: 'Rowdy', age: 0 }

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