CODEWITHSUNDEEP
arraysnode.jsobject
Steve
Steve

Reputation: 75

Node JS Array of Objects - get indexOf

I have an array of objects. I am attempting to locate the index of an object inside this array, however it always returns -1 unless I "cheat". I cannot see the difference here and it console.logs the exact same output both ways. It only works one way... Is this a bug?

var arr = [{ un: 'test', uid: 1 }];
console.log("array",arr,typeof arr);

var obj = { un: 'test', uid: 1};
console.log("obj",obj);

console.log(arr[0],typeof arr[0]);
console.log("indexOf",arr.indexOf(obj));

arr.push(obj);
console.log(arr);
console.log("indexOf",arr.indexOf(obj));

The Output is this:

array [ { un: 'test', uid: 1 } ] object
obj { un: 'test', uid: 1 }
{ un: 'test', uid: 1 } 'object'
indexOf -1
[ { un: 'test', uid: 1 }, { un: 'test', uid: 1 } ]
indexOf 1

For the life of me, I cannot see the difference here. Am I missing something simple here? It's possible... considering the hours of coding, simple things get overlooked.

Upvotes: 0

Views: 611

Answers (1)

Francois
Francois

Reputation: 3080

In javascript, Objects are always references to the object itself (pointers to memory address where the object is stored), so doing 

var arr = [{ un: 'test', uid: 1 }];
var obj = { un: 'test', uid: 1};
console.log("obj",obj);

will never return anything else than -1 because obj has a different address than the object in arr. That's why, if you push objin arr it does work.

So Array.prototype.indexOf with an object as an argument will look for the same reference, whereas Array.prototype.indexOf with number, string, null will look for the value.

If you want to find the index of an object with specific properties use :

var arr = [{ un: 'test', uid: 1 }];
var index = arr.findIndex(i => i.un === 'test' && i.uid === 1);

Here is the doc for findIndex : https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/findIndex

Upvotes: 1

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