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

You can use _.map(), _.assign() and _.find().

// Iterate over first array of objects
_.map(a, function(obj) {

    // add the properties from second array matching the userID
    // to the object from first array and return the updated object
    return _.assign(obj, _.find(b, {userId: obj.userId}));
});

Fiddle Demo

var a = [{
    userId: "p1",
    item: 1
}, {
    userId: "p2",
    item: 2
}, {
    userId: "p3",
    item: 4
}];

var b = [{
    userId: "p1",
    profile: 1
}, {
    userId: "p2",
    profile: 2
}];

var arrResult = _.map(a, function(obj) {
    return _.assign(obj, _.find(b, {
        userId: obj.userId
    }));
});

console.log(arrResult);
document.getElementById('result').innerHTML = JSON.stringify(arrResult, 0, 4);