20+ Output questions in javascript

JavaScript Output Questions Explained

1.What is the output of the following JavaScript code?

console.log(1 + "2" + "2");
console.log(1 + +"2" + "2");
console.log(1 + -"1" + "2");
console.log(+"1" + "1" + "2");
console.log("A" - "B" + "2");
console.log("A" - "B" + 2);

The output of the code will be:

122;
32;
02;
112;
NaN2;
NaN;

Explanation

In the first line, the + operator is used to concatenate the string "2" to the number 1, so the result is the string "12". In the second line, the + operator is used twice: first to convert the string "2" to a number, and then to add that number to 1, so the result is the number 3. In the third line, the - operator is used to convert the string "1" to a number and then subtract that number from 1, so the result is the number 0. In the fourth line, the + operator is used twice: first to convert the string "1" to a number, and then to add that number to the string "1", so the result is the string "11".

In the fifth and sixth lines, the - operator is used to subtract the string "B" from the string "A", which is not a valid operation and therefore produces the special value NaN (not a number). When the NaN value is concatenated with the string "2" in the fifth line, the result is the string "NaN2". When it is added to the number 2 in the sixth line, the result is still NaN.

2. What is the output of the following code, and why?

console.log(typeof null);

The output of the code will be:

"object";

//Because in JavaScript, the data type of null is an object

3. What is the output of the following code, and why?

const array = [1, 2, 3];
for (let i = 0; i < array.length; i++) {
  setTimeout(() => {
    console.log(array[i]);
  }, 1000);
}

The output of the code will be:

3 3 3

// refer how async js work

4. What is the output of the following code, and why?

const foo = {
  bar: function () {
    console.log(this);
  },
};

foo.bar();

const baz = foo.bar;
baz();

5. What is the output of the following code, and why?

const x = 10;
const y = "10";

console.log(x == y);
console.log(x === y);

6. What is the output of the following JavaScript code?

console.log(0.1 + 0.2);

7. What is the result of running the following code?

let x = 10;
let y = "20";
console.log(x + y);

8. Consider the following code:

function greet(name) {
  console.log("Hello " + name);
}

greet("John");

What is the output of this code?

9. What is the output of the following code?

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

10. Consider the following code:

let x = 10;
let y = 20;
console.log(x > y);

What is the output of this code?

11. What is the output of the following JavaScript code?

async function foo() {
  console.log("Hello");
  return "World";
}

async function bar() {
  const result = await foo();
  console.log(result);
}

bar();

The output of this code would be:

Hello;
World;

12. What is the result of running the following code?

async function foo() {
  return Promise.resolve("Hello");
}

async function bar() {
  const result = await foo();
  console.log(result);
}

bar();

The output of this code would be:

Hello;

13. Consider the following code:

async function foo() {
  return Promise.reject("Error");
}

async function bar() {
  try {
    const result = await foo();
    console.log(result);
  } catch (error) {
    console.log(error);
  }
}

bar();

What is the output of this code?

The output of this code would be:

Error;

14. What is the output of the following code?

async function foo() {
  return "Hello";
}

async function bar() {
  const result = await foo();
  console.log(result);
}

const result = bar();
console.log(result);

The output of this code would be:

Hello
Promise { "Hello" }

15. Consider the following code:

async function foo() {
  return "Hello";
}

async function bar() {
  const result = await foo();
  console.log(result);
}

bar()
  .then((result) => console.log(result))
  .catch((error) => console.log(error));

16.What is the output of this code?

The output of this code would be:

Hello;
Hello;