Underscore filter function which returns the indexes instead

filterIndexes.js

const _ = require('underscore')

function filterIndexes(collection, selector) {
  var results = [],
      predicate = _.matcher(selector);

  // Works just like _.filter, but returns the indexes instead
  _.each(collection, function (value, index, list) {
    if (predicate(value, index, list)) {
      results.push(index);
    }
  });

  return results;
}