Function sometimes saying an object doesnt exist in an array of arrays, when it does

Question

i have an array, filled with arrays containing multiple objects. I have a function that returns if an object exists in there or not, but sometimes it cant find an object that is definitely in there. I put a ton of console logs so i can keep track of everything and show you the console. Here is the code:

var adjacent = inChain(x, y - 1, array);
array[adjacent].push({x: x, y: y})

So here i call the inChain function which searches for the object and then returns the index its in. The error is on the 2nd line at push as if it cant find it, adjacent will be null.

Function:

function inChain(x, y, array)
{
    var currentPiece = {x: x, y: y};
    
    console.log("checking array below");
    console.log(array);
    console.log("checking if this object exists");
    console.log(currentPiece);
    
    for(let i = blackChains.length; i--;)
    {
        for(let j = blackChains[i].length; j--;)
        {
            if (JSON.stringify(blackChains[i][j]) === JSON.stringify(currentPiece))
            {
                console.log("it does at " + i);
                return i;
            }
        }
    }    
    console.log("doesnt exist");
    return null;
}

So as you can see by the console logs, it will say each step, first it will show the array its looking in, then the object its looking for. heres a screenshot of it in action:

So you can see the array contains 1 array which contains 1 object. An object with the properties x: 3, y: 2

Then you can see the object its searching for, an object with the exact same properties

Would anyone know why its sometimes not finding it? and sometimes it does?

I think the comparison using `JSON.stringify()` is not stable enough. Consider creating some hash-function and compare by the hash values of your objects. — Sirko, Jun 01 '17 at 09:44
in this case x would be 3, y would be 3 and the array would be the array that contains all the objects in this case. it would search for x, y-1 in that array so it becomes 3,2, array — Slavik Ribz, Jun 01 '17 at 09:46
Do you think its because of the JSON.stringify? i thought that too but im not sure — Slavik Ribz, Jun 01 '17 at 09:46
`a= {}; a.x = 1; a.y=2; b={}; b.y=2; b.x=1;` leads to `JSON.stringify(a) != JSON.stringify(b)` although a comparison for each individual property says otherwise. — Sirko, Jun 01 '17 at 09:48
i don't get why you receive an array in your parameter, then use the blackchain array — Deblaton Jean-Philippe, Jun 01 '17 at 09:50
@Sirko mines not like that though, the x and y are the correct way round — Slavik Ribz, Jun 01 '17 at 09:51
@DeblatonJean-Philippe ohhhh i think you might have cracked it — Slavik Ribz, Jun 01 '17 at 09:51
Check [this](https://stackoverflow.com/questions/24841476/cannot-read-property-push-of-undefined-weird-error) out.. You are trying to `push` at an index of `array` which doesn't exist. — Sandman, Jun 01 '17 at 09:53
@Sandman the error was i was trying to push at an undefined index, the program didnt know which index i wanted — Slavik Ribz, Jun 01 '17 at 09:54
try to use array.prototype.findIndex instead of your for loop, it's more readable, and compare the values, instead of the stringification — Deblaton Jean-Philippe, Jun 01 '17 at 09:54

Function sometimes saying an object doesnt exist in an array of arrays, when it does

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