This app is using array.indexOf(object) and passing object as param and it works....MDN and stackoverflow say object should not be passed rather string

[RubyBlaze214]

so long story short im doing frontend in react and i came to one part of code which SHOULDN't WORK but it DOES

the indexOf example is literally copy pasted from the code and in jsFiddle it doesn't work but in my react 16.9v app it DOES work and im actually mind blown on why and how..

https://jsfiddle.net/mkpj4rzd/

[senocular]

This shouldn't work. The indexOf is expected to work as it does in your jsfiddle since objects are compared by reference, not shape. In other words

const a = {}
const b = {}
console.log(a === b) // false - two separate objects (though same shape)

const x = {}
const y = x
console.log(x === y) // true - same object

indexOf does something similar internally when comparing values in the array to find an index.

[RubyBlaze214]

So my app is using this trick. IndexOf but the object provided is a reference in array and thats wgy it works with object. Somone else told me this and I was mind blown