I'm a bit stuck with something (hoping simple), maybe someone here can have a look and point that simple thing I'm missing. I am getting some objects and wanna push them to an array. on push, getting the error: Cannot add property 0, object is not extensible

if (keysLength > 0) {
    //@ts-ignore
    let Arr = [];

    for(let x = 0; x < keysLength; x++) {
        let keys = "item" + x;
        // getting all the items from storage 
        // and merging into 1 array
        chrome.storage.sync.get([keys], function(result) {
            // err: Cannot add property 0, object is not extensible
            Arr.push(result[keys]);
        });
        if (x === keysLength-1){
            console.log(Arr)
        }
    }
}

appreciate the time