Javascript indexOf object not found - Stack Overflow

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I'm trying to find the index of my object inside an array in Javascript.

This is the code I'm using, this returns -1 so it's not found. But it's there

var index = this.state.users.indexOf(user);

The object I'm paring with is identical to the one's in the collection as shown in the picture below

I'm using this code to pare the two

console.log(this.state.users[0]);
console.log(member);

So I don't understand why this is giving a negative result

I'm trying to find the index of my object inside an array in Javascript.

This is the code I'm using, this returns -1 so it's not found. But it's there

var index = this.state.users.indexOf(user);

The object I'm paring with is identical to the one's in the collection as shown in the picture below

I'm using this code to pare the two

console.log(this.state.users[0]);
console.log(member);

So I don't understand why this is giving a negative result

• javascript
• indexof

Share Improve this question Follow edited Nov 29, 2019 at 14:09 Federico klez Culloca 27.2k1717 gold badges6060 silver badges102102 bronze badges asked Aug 5, 2015 at 11:45 Miguel StevensMiguel Stevens 9,2501919 gold badges7575 silver badges136136 bronze badges 4

• 1 So, just to be clear, you want to find the index of an Object in Array? – Lucian Commented Aug 5, 2015 at 11:51
• Maybe you can try something like this stackoverflow./a/7178381/5182914 – bloC Commented Aug 5, 2015 at 11:56
• Hi, The following worked for me, the filter function reddit./r/javascript/ments/3fv2ou/… – Miguel Stevens Commented Aug 5, 2015 at 11:58
• I added my answer below. – Lucian Commented Aug 5, 2015 at 12:02

Add a ment  | 

7 Answers 7

Sorted by: Reset to default 2

In javascript object pared by reference, such as

var obj1 = {prop: 0};
var obj2 = {prop: 0};
alert(obj1 === obj2); //false

indexOf pare like this, so it isn't finding anything.

To find object in array identical to given, you can use Array.prototype.filter method.

Or ecmascript 2015 Array.prototype.find method

Array indexOf uses STRICT EQUALITY (===)

so

var v1 = {id:1, info:{something:'else'}};
var v2 = {id:2, info:{something:'else'}};
var v3 = {id:1, info:{something:'else'}};
var v4 = v2;
var arr = [v1, v2];
arr.indexOf(v2); // 1
arr.indexOf(v3); // -1
arr.indexOf(v4); // 1

even though v3 looks just like v1, it's not v1

so it depends on how the object you are trying to find is related to the objects in the array

IndexOf function is used to find an occurrence of a string in another one.

When this occurrence is not found, the function return -1.

Please refer to this website for more informations :

http://www.w3schools./jsref/jsref_indexof.asp

It returns -1 if it never occurs.

http://www.w3schools./jsref/jsref_indexof.asp

It uses strict parison to find member in the users array.

What it means is that if it will return -1 if for every entry in your array member !== theUserYouAreLookingFor (which is the case when variables are not holding reference to the same object, not similar but the same object in memory).

You need a custom function for something like this, in which you pass the array you want to search in, the object you want to find the index for and a unique property of the object:

var indexOfArrayObject = function(arr, obj, prop) {
    var index = -1;
    arr.some(function(val, ind){
        if(val[prop] === obj[prop]) {
            index = ind;
            return true;
        }
    });
    return index;
}

// Getting the index by 'id'
var userIndex = indexOfArrayObject(this.state.users, user, 'id');

Because, in JavaScript, { a: 1 } === { a: 1 } or { a: 1 } == { a: 1 } is false.

In your environment, you'll also find that this.state.users[0] === member is false too.

So, the method you're using for parison is not correct.

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