merge sorted arrays

function mergeSortedArrays(array1,array2)
{
    const mergedArray = [];
    //Check input
    if(array1.length === 0)
    {
        return array2;
    }
    if(array2.length === 0)
    {
        return array1;
    }
    if(array1.length === 0 && array2.length === 0)
    {
        return mergedArray;
    }
    let array1Item = array1[0];
    let array2Item = array2[0];
    let array1Index = 1;
    let array2Index = 1;
    while(array1Item || array2Item)
    {
        if(!array2Item || array1Item < array2Item)
        {
            mergedArray.push(array1Item);
            array1Item = array1[array1Index];
            array1Index++;
        }
        else 
        {
            mergedArray.push(array2Item);
            array2Item = array2[array2Index];
            array2Index++;
        }
        
    }
    return mergedArray;
    
    
}
console.log(mergeSortedArrays([0,3,4,31],[4,6,30]));