deep-extend array merge when key values exist

gistfile1.ts

function merge(key: string, ...arrays: Array<any>[]) {

    // skip trivial arrays
    arrays = arrays.filter(a => !!a && 0 < a.length);
    var result = arrays.shift();
    if (!arrays.length) return result;

    var hash = {}; result.forEach((item, i) => hash[item.id] = i);

    arrays.forEach(array => {
        array.forEach(item => {
            var id = item[key];
            if (typeof hash[id] === "undefined") {
                hash[id] = result.push(item) - 1;
            } else {
                result[hash[id]] = deepExtend(result[hash[id]], item);
            }
        });
    });

    return result;
}

/*
  Modify deepExtend to call merge when two arrays are encountered:
            } else if (Array.isArray(val)) {
                target[key] = merge("id", target[key], deepCloneArray(val));
                return;
*/