What is the difference between filter and map functions in JavaScript?

What is the difference between filter and map functions in JavaScript?

The filter function 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 functions?

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: [2, 4]

For map, if you want to double each number:

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

Are there any performance differences between them?

Yes, there can be performance differences. filter may be slower if the array is large because it needs to evaluate each element to determine if it should be included. map is generally faster since it simply transforms each element without any condition.

When should I use one over the other?

Use filter when you need to select a subset of elements based on a condition, and use map when you want to transform each element in the array.