How to get the index of an object in an array of objects when it matches completely javascript

Question

I have an array of objects and I would like to get the index of the object in the array when I get a match.

I have the array as follows:

let x = [
{name: "emily", info: { id: 123, gender: "female", age: 25}},
{name: "maggie", info: { id: 234, gender: "female", age: 22}},
{name: "kristy", info: { id: 564, gender: "female", age: 26}},
 .....
];

Currently I am using indexOf which worked initially and now it doesn't work properly. It returns -1.

let find = {name: "maggie", info: { id: 234, gender: "female", age: 22}};
let index = x.indexOf(find); // should return 1.

The whole should match in the array and should return the index of that object. How can I achieve this? Should I be using some() ?

Thank you

https://stackoverflow.com/questions/1068834/object-comparison-in-javascript — sakthi, Aug 01 '18 at 06:11

Sushanth -- · Answer 1 · 2018-08-01T18:35:48.137

2

You can use .find instead of indexOf as 2 objects are never equal ( as they point to different reference in memory ) which is what you seem to pass as an argument.

let x = [
{name: "emily", info: { id: 123, gender: "female", age: 25}},
{name: "maggie", info: { id: 234, gender: "female", age: 22}},
{name: "kristy", info: { id: 564, gender: "female", age: 26}}
];

let found = x.find(function(item) {
  // you can use the condition here
  return item.info.id === 564;
});

console.log(found);

To find the index, you can use .findIndex method instead.

let x = [
    {name: "emily", info: { id: 123, gender: "female", age: 25}},
    {name: "maggie", info: { id: 234, gender: "female", age: 22}},
    {name: "kristy", info: { id: 564, gender: "female", age: 26}}
];

let foundIndex = x.findIndex(function(item) {
  // you can use the condition here
  return item.info.id === 564;
});

console.log(foundIndex);

edited Aug 01 '18 at 18:35

answered Aug 01 '18 at 01:06

Sushanth --

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The poster specifies that they are seeking "the index of that object." `find` returns the object itself. – aaplmath Aug 01 '18 at 01:14
Seems like the id in the example is a bit misleading. What if there is nothing like a unique identifier. I just want to compare everything and return the index where every property is equal? – Angela Roux Aug 01 '18 at 05:02
1

@AngelaRoux You should then change a logic of the application as it will create more and more issues as you go. If you really need to, this [question](https://stackoverflow.com/questions/201183/how-to-determine-equality-for-two-javascript-objects) might come handy. – Dawid Zbiński Aug 01 '18 at 06:00

score 0 · Answer 2 · answered Aug 01 '18 at 01:11

Objects cannot be compared by traditional equality in JavaScript. Instead, use the ES6 findIndex method to compare each object's properties with the desired values. Here is an example:

let x = [
{name: "emily", info: { id: 123, gender: "female", age: 25}},
{name: "maggie", info: { id: 234, gender: "female", age: 22}},
{name: "kristy", info: { id: 564, gender: "female", age: 26}}
];
let find = {name: "maggie", info: { id: 234, gender: "female", age: 22}};
let index = x.findIndex(element => element.info.id === find.info.id); // index === 1

The id value seems to be sufficient to identify an object in your scenario; if you need to compare more properties, you could obviously add additional equality checks (e.g., element.name === find.name) with the && operator.

findIndex doesn't work in IE 11 and also what if the id is not a unique identifier, I want to compare all of the properties in the object with the object passed in and return the index if everything is a match. — Angela Roux, Aug 01 '18 at 05:03

Akrion · Answer 3 · 2018-08-01T06:23:19.817

If we live in the _.lodash world than this works since lodash would go deep on objects:

let data = [
{name: "emily", info: { id: 123, gender: "female", age: 25}},
{name: "maggie", info: { id: 234, age: 22, gender: "female"}},
{name: "kristy", info: { id: 564, gender: "female", age: 26}},
];

let find = {name: "maggie", info: { id: 234, gender: "female", age: 22}};
let index = _.findIndex(data, (i) => _.isEqual(i, find))

console.log(index)  // 1

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.10/lodash.min.js"></script>

A more brutish approach which obviously it is not performant and as pointed out wont work if the order of the props is different.

let data = [
{name: "emily", info: { id: 123, gender: "female", age: 25}},
{name: "maggie", info: { id: 234, gender: "female", age: 22}},
{name: "kristy", info: { id: 564, gender: "female", age: 26}},
];

var objectJSONs = data.map((i) => JSON.stringify(i))

let myJSON = JSON.stringify({name: "maggie", info: { id: 234, gender: "female", age: 22}});
let index = objectJSONs.indexOf(myJSON)

console.log(index) // 1

Added a `lodash` solution which works regardless of the order. Now it is not vanilla JS etc but he should have as many options as possible to chose from :) — Akrion, Aug 01 '18 at 06:26

sakthi · Answer 4 · 2018-08-01T06:28:15.947

You can make use of underscore _.isEqual for Object comparison and some() or any looping mechanism to iterate the array.

let iFoundIndex = -1;
let bFound = x.some((data,index) => {
                    if(_.isEqual(data,find){
                        iFoundIndex = index;
                        return true;
                    }
                    return false;
                  }
 //console.log(iFoundIndex);

How to get the index of an object in an array of objects when it matches completely javascript

4 Answers4