What is an 'Array-like Object?'

Question 1

What is an ‘array-like object’ in JavaScript?

Answer 1

An object that has indexed access (elements can be accessed using numerical indexes like myObj[0]) and a length property, but lacks most built-in array methods (like push, pop, map, filter). It’s not a true array.

Question 2

Give two common examples of array-like objects in JavaScript.

Answer 2

1. The arguments object (inside non-arrow functions). 2. NodeList (from document.querySelectorAll()).

Question 3

Why are array-like objects less convenient than true arrays?

Answer 3

They don’t have built-in array methods (like push, pop, map, filter, etc.).

Question 4

How can you convert an array-like object into a real JavaScript array? Give two methods.

Answer 4

1. Array.from(arrayLike, mapFn?)
2. Spread syntax (…arrayLike)

Question 5

Explain how to use Array.from() to convert the arguments object to a real array and double each value.

Answer 5

function myFunction() {
const argsArray = Array.from(arguments, (arg) => arg * 2);
return argsArray;
}
console.log(myFunction(1, 2, 3)); // Output: [2, 4, 6]

Question 6

Explain how to use the spread syntax to convert a NodeList to a real array.

Answer 6

const nodeList = document.querySelectorAll(‘li’);
const nodeArray = […nodeList];

Question 7

What are the benefits of converting an array-like object to a real array?

Answer 7

• You can use all built-in array methods.
• The code becomes more readable.
• It’s a modern JS best practice.

Question 8

What is a potential downside to converting an array-like object?

Answer 8

Performance: Converting a very large array-like object into an array might have a slight performance cost.

Question 9

True or false: Array-like objects inherit from Array.prototype.

Answer 9

False. They lack standard array methods because they don’t inherit from Array.prototype.

Question 10

What happens if you try to use an array method directly on an array-like object (e.g., arguments.push(4))?

Answer 10

You’ll get a TypeError, because array-like objects don’t have Array methods until converted.