JavaScript Fundamentals Screen

What they ask

For junior software roles the technical interview is a JavaScript fundamentals and problem-solving session, reported as roughly three theory questions and three problem-solving questions. Topics named by candidates: closures, scope, hoisting, the event loop, promises and async behavior, and basic data structures.

Theory questions in this area, for example:

• What does this print, and why: a console.log inside setTimeout(..., 0), one inside Promise.resolve().then(...), and one at top level?
• Why does a var in a loop with closures print the same value, and how do let or an IIFE fix it?
• What is hoisting for var, let, const and function declarations?

Problem-solving sample (solve in the starter code): flatten a nested array of arbitrary depth without using Array.prototype.flat.

Examples

• [1, [2, [3, [4]]], 5] returns [1, 2, 3, 4, 5].
• [[], [[]], 1] returns [1].

Constraints

• Up to 10^4 total elements; depth up to 1,000 (so consider an iterative stack).

What they look for

• Explaining the event loop order out loud (call stack, microtasks, then macrotasks).
• Handling edge cases (empty arrays, non-array values) without prompting.
• Both a recursive and an iterative version if asked.