[рони]

desperado,
вариант

var array1 = [1, 2, 3, 4, 5],
    array2 = [0, 7, 1, 2, 3];

function foo(arr1, arr2) {
    var diff = [];
    for (var i = 0; i < arr2.length; i++) {
        if (arr1[i] != arr2[i]) {
            diff.push(arr2.shift());
            i = 0
        }
    }
    return diff
}
alert(foo(array1, array2))