5 JavaScript Output-Based Problems to Practice Before Your Next Interview

JavaScript output-based questions are a staple in coding interviews. They test your understanding of core concepts like hoisting, closures, async operations, and object immutability.

Here are five tricky problems you should master:

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1. What will the following code output, and why?

console.log(a);
var a = 10;
console.log(b);
let b = 20;

Answer:

undefined

ReferenceError: Cannot access ‘b’ before initialization

Explanation:

1. var a: Variables declared with var are hoisted to the top of their scope and initialized with undefined. Hence, console.log(a) outputs undefined.

2. let b: Variables declared with let are also hoisted, but they remain in the “temporal dead zone” until their declaration is encountered. Accessing b before its declaration results in a ReferenceError.

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2. What will the following code output, and how can you ensure a deep copy?

let obj1 = {
name: 'John',
address: {
city: 'New York',
zip: '10001'
}
};
let obj2 = {…