How to use Lodash to merge two collections based on a key?

Question

I have two collections, and the objects have a common key \"userId\". As below:

var _= require(\'lodash\');

var a = [
  { userId:\"p1\", item:1},
  { userId         


        

Answer 1

Just for completeness: A proposal without any library.

function merge(a, b, key) {

    function x(a) {
        a.forEach(function (b) {
            if (!(b[key] in obj)) {
                obj[b[key]] = obj[b[key]] || {};
                array.push(obj[b[key]]);
            }
            Object.keys(b).forEach(function (k) {
                obj[b[key]][k] = b[k];
            });
        });
    }

    var array = [],
        obj = {};

    x(a);
    x(b);
    return array;
}

var a = [
        { userId: "p1", item: 1 },
        { userId: "p2", item: 2 },
        { userId: "p3", item: 4 }
    ],
    b = [
        { userId: "p1", profile: 1 },
        { userId: "p2", profile: 2 }
    ],
    c = merge(a, b, 'userId');

document.write('
' + JSON.stringify(c, 0, 4) + '
');