Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

JavaScript JavaScript Array Iteration Methods Combining Array Methods Chaining Array Methods

Teri Dent
Teri Dent
11,515 Points
Posted by Teri Dent
Teri Dent
11,515 Points

Filter Parameters

Looking at the code for the filter unique items at the bottom of the teacher's notes:

const numbers = [1, 1, 2, 3, 4, 3, 5, 5, 6, 7, 3, 8, 9, 10];

const unique = numbers.filter(function(number, index, array) { return index === array.indexOf(number); });

console.log(unique); // => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Is the inclusion of the array parameter in the filter function for scope purposes? That is, would the filter function not have access to the indexOf() without providing this parameter?

Thank you.

2 Answers

Steven Parker
Steven Parker
231,268 Points
Steven Parker
Steven Parker
231,268 Points

That's right, without the 3rd parameter the function would only have access to the value ("number") and the index, but not to the array they came from.

Teri Dent
Teri Dent
11,515 Points
Teri Dent
Teri Dent
11,515 Points

Many thanks Steven.