mergeArraysKeepOrder.js

function mergeArraysKeepOrder(a1, a2) {
    var a = [];
    var i = 0, j = 0;
    while (true) {
        for (; i < a1.length; i++) {
            if (a2.indexOf(a1[i], j) != -1) {
                i++;
                break;
            }
            a.push(a1[i]);
        }
        for (; j < a2.length; j++) {
            if (a1.indexOf(a2[j], i) != -1) {
                j++;
                break;
            }
            a.push(a2[j]);
        }
        if (i == a1.length && j == a2.length) {
            break;
        }
    }
    return a;
}