P7.1: Technical Mock Interviews

Landing a software engineering role requires more than coding skills. You must be able to explain your technical decisions clearly under interview pressure.

In this lesson, we will cover the core JavaScript, React, and browser networking questions that recur in technical mock interviews.

1. Core JavaScript Conceptual Questions

Question 1: What is a Closure in JavaScript?

A closure is the combination of a function bundled together with references to its surrounding state (the lexical environment). In other words, a closure gives an inner function access to the outer function's scope even after the outer function has returned.

function makeCounter() {
  let count = 0; // Lexical scope variable
  return function() {
    count++; // Accesses parent variable
    return count;
  };
}

const counter = makeCounter();
console.log(counter()); // 1
console.log(counter()); // 2

Question 2: What is the Event Loop?

JavaScript is single-threaded. The Event Loop is the mechanism that allows JavaScript to perform non-blocking operations by offloading tasks (like timers, network requests) to the browser web APIs, and then pushing callback functions onto the call stack when the stack is empty.

2. React Core Interview Focus

Question: What is the difference between state and props?

• Props: Configuration parameters passed down from a parent component. They are read-only (immutable) and cannot be modified by the component that receives them.
• State: Local data storage managed within the component itself. State changes trigger component re-rendering and are mutable via the setter function (setState / useState).

3. High-Frequency Interview Practice Sheet

Make sure you can comfortably explain the following concepts:

• CSS Specificity: How the browser decides which styles to apply based on selectors types (IDs > Classes > Tags).
• Promise vs Async/Await: Syntactic differences in handling asynchronous JavaScript.
• CORS Errors: Why browsers block cross-origin requests and how CORS headers resolve it.