Get index in an array.filter callback function

Question

I have the following array filter with a callback function:

array.filter(createPredicateFn(expression, comparator));

My call back function is declared as follow:

function createPredicateFn(expression, comparator) {

How can I get the index of the element inside my createPredicateFn?

Edit:

here is my predicate function:

     function createPredicateFn(expression, comparator) {
            var predicateFn;

            if (comparator === true) {
                comparator = angular.equals;
            } else if (!angular.isFunction(comparator)) {
                comparator = function (actual, expected) {
                    if (angular.isObject(actual) || angular.isObject(expected)) {
                        // Prevent an object to be considered equal to a string like `'[object'`
                        return false;
                    }

                    actual = angular.lowercase('' + actual);
                    expected = angular.lowercase('' + expected);
                    return actual.indexOf(expected) !== -1;
                };
            }

            predicateFn = function (item) {
                return deepCompare(item, expression, comparator);
            };

        }

Answer 1

Within your createPredicateFn() you have to return another function. This inner function can have up to three parameters:

1. the value of the element
2. the index of the element
3. the Array object being traversed

(Source: MDN)

Hence the second parameter of your inner function is the index you look for.

A simplistic example could look like this:

function createPredicateFn(expression, comparator) {
  return function( val, index, arr ) {
    // do something and return a boolean here
    return index % 2 == 0;
  }
}