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

I don't know if there is an existing underscore method that does this, but you can achieve the same result with plain javascript.

Array.prototype.getIndexBy = function (name, value) {
    for (var i = 0; i < this.length; i++) {
        if (this[i][name] == value) {
            return i;
        }
    }
    return -1;
}

Then you can just do:

var data = tv[tv.getIndexBy("id", 2)]

Answer 2

Keepin' it simple:

// Find the index of the first element in array
// meeting specified condition.
//
var findIndex = function(arr, cond) {
  var i, x;
  for (i in arr) {
    x = arr[i];
    if (cond(x)) return parseInt(i);
  }
};

var idIsTwo = function(x) { return x.id == 2 }
var tv = [ {id: 1}, {id: 2} ]
var i = findIndex(tv, idIsTwo) // 1

Or, for non-haters, the CoffeeScript variant:

findIndex = (arr, cond) ->
  for i, x of arr
    return parseInt(i) if cond(x)

Answer 3

The simplest solution is to use lodash:

1. Install lodash:

npm install --save lodash

2. Use method findIndex:

const _ = require('lodash');

findIndexByElementKeyValue = (elementKeyValue) => {
  return _.findIndex(array, arrayItem => arrayItem.keyelementKeyValue);
}

Answer 4

you can use indexOf method from lodash

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

Answer 5

I got similar case but in contrary is to find the used key based on index of a given object's. I could find solution in underscore using Object.values to returns object in to an array to get the occurred index.

var tv = {id1:1,id2:2};
var voteIndex = 1;
console.log(_.findKey(tv, function(item) {
  return _.indexOf(Object.values(tv), item) == voteIndex;
}));

<script src="https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.9.1/underscore-min.js"></script>

Answer 6

If you're expecting multiple matches and hence need an array to be returned, try:

_.where(Users, {age: 24})

If the property value is unique and you need the index of the match, try:

_.findWhere(Users, {_id: 10})