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JavaScript JavaScript Array Iteration Methods Combining Array Methods Chaining Array Methods

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
218,812 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

Many thanks Steven.