I wrote a extender function to observableArray in knockout js. What I'm looking for is a way to extract the intersection records based on one property. This works well on smaller number of arrays, but shows pretty poor performance in larger arrays. I dont know if it is the observables that makes it slower?

How would you guys write it?

obsArray2 - The array to compare with

Key - Name of the property to compare between

ko.observableArray.fn.intersect = function (obsArray2, Key) {
    var self = Enumerable.From(ko.unwrap(this));
    var arrValues1 = self.Select(function (item) { return ko.unwrap(item[Key]); });
    arrValues2 = Enumerable.From(ko.unwrap(obsArray2)).Select(function (item) { return ko.unwrap(item[Key]); });
    var IntersectedValues = arrValues1.Intersect(arrValues2).ToArray();

    return self.Where(function (item) { return IntersectedValues.contains(ko.unwrap(item[Key])) }).ToArray();
    return obsArray1.Intersect(obsArray2).ToArray();

1 Answer 1


I would not use linq.js for anything time sensitive, it is known to be slow, definitely compared to just using old skool for loops and arrays. Which is what I would use.

Other than, if I were to write this, I would consider naming some thing differently:

  • obsArray2 -> observableArray, there is no obsArray1, and it was not clear at first if obs means there are objects in the array or it is an observable arrays.
  • self -> anything but self which usually refers to this, perhaps enum1 ?
  • arrValues1 really contains an Enumerable which is not really an array, confusing, I would perhaps have chosen set1 because in maths, intersections are made of sets or enum1 because that is what the variable type is
  • Same for arrValues2 of course
  • intersectedValues -> I would have gone for simply intersection


  • You have 2 return statements, there can be only one
  • It seems silly to go back to self and filter out only elements that are in the intersection, can't you build the return value from intersectedValues ?
  • \$\begingroup\$ Thank you. Naming variables is a skill i really lack. Thank you for great pointers! What would you use linqjs for? Smaller tasks? \$\endgroup\$
    – Pochen
    Commented Dec 5, 2014 at 8:40
  • \$\begingroup\$ I would use linqjs for complex operations with little volume. \$\endgroup\$
    – konijn
    Commented Dec 5, 2014 at 15:34

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