javascript - Merge property from an array of objects into another based on property value lodash

Question

I have 2 arrays of objects, they each have an id in common. I need a property from objects of array 2 added to objects array 1, if they have matching ids.

Array 1:

[
    {
        id: 1,
        name: tom,
        age: 24
    },
    {
        id: 2,
        name: tim,
        age: 25
    },
    {
        id: 3,
        name: jack,
        age: 24
    },

]

Array 2:

[
    {
        id: 1,
        gender: male,
        eyeColour: blue,
        weight: 150
    },
    {
        id: 2,
        gender: male,
        eyeColour: green,
        weight: 175
    },
    {
        id: 3,
        gender: male,
        eyeColour: hazel,
        weight: 200
    },

]

Desired Outcome:

[
    {
        id: 1,
        name: tom,
        age: 24,
        eyeColour: blue,
    },
    {
        id: 2,
        name: tim,
        age: 25,
        eyeColour: green,
    },
    {
        id: 3,
        name: jack,
        age: 24,
        eyeColour: hazel,
    },

]

I tried using lodash _.merge function but then I end up with all properties into one array, when I only want eyeColour added.

Answer 1

Lodash remains a highly useful bag of utilities, but with the advent of ES6 some of its use cases are less compelling.

For each object (person) in the first array, find the object in the second array with matching ID (see function findPerson). Then merge the two.

function update(array1, array2) {
  var findPerson = id => array2.find(person => person.id === id);

  array1.forEach(person => Object.assign(person, findPerson(person.id));
}

For non-ES6 environments, rewrite arrow functions using traditional syntax. If Array#find is not available, write your own or use some equivalent. For Object.assign, if you prefer use your own equivalent such as _.extend.

This will merge all properties from array2 into array1. To only merge eyeColour:

function update(array1, array2) {
  var findPerson = id => array2.find(person => person.id === id);

  array1.forEach(person => {
    var person2 = findPerson(person.id));
    var {eyeColour} = person2;
    Object.assign(person, {eyeColour});
  });
}