find the array index of an object with a specific key value in underscore

Question

In underscore, I can successfully find an item with a specific key value

var tv = [{id:1},{id:2}]
var voteID = 2;
var data = _.find(tv, function(voteItem){ r         


        

Answer 1

If you want to stay with underscore so your predicate function can be more flexible, here are 2 ideas.

Method 1

Since the predicate for _.find receives both the value and index of an element, you can use side effect to retrieve the index, like this:

var idx;
_.find(tv, function(voteItem, voteIdx){ 
   if(voteItem.id == voteID){ idx = voteIdx; return true;}; 
});

Method 2

Looking at underscore source, this is how _.find is implemented:

_.find = _.detect = function(obj, predicate, context) {
  var result;
  any(obj, function(value, index, list) {
    if (predicate.call(context, value, index, list)) {
      result = value;
      return true;
    }
  });
  return result;
};

To make this a findIndex function, simply replace the line result = value; with result = index; This is the same idea as the first method. I included it to point out that underscore uses side effect to implement _.find as well.