How to calculate intersection of multiple arrays in JavaScript? And what does [equals: function] mean?

Question

I am aware of this question, simplest code for array intersection but all the solutions presume the number of arrays is two, which cannot be certain in my case.

I ha

Answer 1

I wrote a helper function for this:

function intersection() {
  var result = [];
  var lists;

  if(arguments.length === 1) {
    lists = arguments[0];
  } else {
    lists = arguments;
  }

  for(var i = 0; i < lists.length; i++) {
    var currentList = lists[i];
    for(var y = 0; y < currentList.length; y++) {
        var currentValue = currentList[y];
      if(result.indexOf(currentValue) === -1) {
        var existsInAll = true;
        for(var x = 0; x < lists.length; x++) {
          if(lists[x].indexOf(currentValue) === -1) {
            existsInAll = false;
            break;
          }
        }
        if(existsInAll) {
          result.push(currentValue);
        }
      }
    }
  }
  return result;
}

Use it like this:

intersection(array1, array2, array3, array4); //["Lorem"]

Or like this:

intersection([array1, array2, array3, array4]); //["Lorem"]

Full code here

UPDATE 1

A slightly smaller implementation here using filter