What is the difference between filter and map in JavaScript?

What is the difference between filter and map in JavaScript?

The filter method creates a new array with all elements that pass the test implemented by the provided function, while map creates a new array with the results of calling a provided function on every element in the calling array.

Can you give me an example of how to use both methods?

Sure! For filter, you might have an array of numbers and want to keep only the even ones:

const numbers = [1, 2, 3, 4, 5];
const evens = numbers.filter(num => num % 2 === 0);
// evens is [2, 4]

For map, if you want to double each number:

const doubled = numbers.map(num => num * 2);
// doubled is [2, 4, 6, 8, 10]

Are there any performance differences between them?

Yes, there can be performance differences. filter may be slower if you're working with large arrays because it creates a new array based on a condition, while map always processes every element. However, the actual performance can depend on the specific use case and the JavaScript engine.

When should I use filter instead of map?

Use filter when you want to reduce the size of an array based on a condition, and use map when you want to transform each element of the array without changing its size.