// iteration function, make array listed by layer from low to high
for(var m = 0; m < arr.length - 1; m++) {
    for (var n = 0; n < arr.length - m - 1; n ++) {
        if (arr[n].layer > arr[n + 1].layer ) {
            swapArr(arr, n, n + 1);
        } 
    }
}

// swap elements in arr
function swapArr(arr, i1, i2) {
    arr[i1] = arr.splice(i2, 1, arr[i1])[0];
    return arr;
}