Question 1

What is the output of const obj = { x: 10, foo: () => console.log(this.x) }; obj.foo()?

Accepted Answer

undefined. Arrow functions inherit this from their lexical scope, not from the object. The enclosing scope's this does not have x. Use a regular function for methods: foo() { console.log(this.x); }.

Question 2

What is the output of console.log('1'); setTimeout(() => console.log('2'), 0); Promise.resolve().then(() => console.log('3')); console.log('4')?

Accepted Answer

1, 4, 3, 2. Sync code (1, 4) runs first. Then microtasks (3, Promise.then). Then macrotasks (2, setTimeout). This is the fundamental event loop order.

Question 3

What is the output of for (var i = 0; i < 3; i++) setTimeout(() => console.log(i), 0)?

Accepted Answer

3, 3, 3. var is function-scoped; all callbacks share one i, which is 3 by the time they run. Use let to fix (logs 0, 1, 2).

Question 4

What is the output of async function with await and console.log?

Accepted Answer

1, 3, 2. Code before await runs synchronously (1). await pauses the function and schedules the rest as a microtask. Code after the foo() call runs (3). Then the rest of foo runs (2, microtask).

What is the output of const obj = { x: 10, foo: () => console.log(this.x) }; obj.foo()?

More FAQs in JavaScript Interview: Output Prediction Questions

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