Join two objects by key in JavaScript

Suppose, we have two child and parent JSON arrays of objects like these −

const child = [{    id: 1,    name: 'somename',    parent: {       id: 2    }, }, {    id: 2,    name: 'some child name',    parent: {       id: 4    } }]; const parent = [{    id: 1,    parentName: 'The first',    child: {} }, {    id: 2,    parentName: 'The second',    child: {} }, {    id: 3,    parentName: 'The third',    child: {} }, {    id: 4,    parentName: 'The fourth',    child: {} }];

We are required to write a JavaScript function that takes in these two arrays.

And our function should merge the child array objects into corresponding parent objects.

Therefore, the final output should look something like this −

const output = [    {       id: 1,       parentName: The first,       child: {}    },    {       id: 2,       parentName: The second,       child: {          id: 1,          name: somename,       }    },    {       id: 3,       parentName: The third,       child: {}    },    {       id: 4,       parentName: The fourth,       child: {          id: 2          name: some child name,       }    }, ];

Example

The code for this will be −

const child = [{    id: 1,    name: 'somename',    parent: {       id: 2    }, }, {    id: 2,    name: 'some child name',    parent: {       id: 4    } }]; const parent = [{    id: 1,    parentName: 'The first',    child: {} }, {    id: 2,    parentName: 'The second',    child: {} }, {    id: 3,    parentName: 'The third',    child: {} }, {    id: 4,    parentName: 'The fourth',    child: {} }]; const combineParentChild = (parent, child) => {    const combined = [];    for (let i = 0; i < parent.length; i++) {       for (let j = 0; j < child.length; j++) {          if (child[j].parent.id === parent[i].id) {             parent[i].child.id = child[j].id;             parent[i].child.name = child[j].name;             break;          };       };       combined.push(parent[i])    };    return combined; }; console.log(combineParentChild(parent, child));

Output

And the output in the console will be −

[    { id: 1, parentName: 'The first', child: {} },    {       id: 2,       parentName: 'The second',       child: { id: 1, name: 'somename' }    },    { id: 3, parentName: 'The third', child: {} },    {       id: 4,       parentName: 'The fourth',       child: { id: 2, name: 'some child name' }    } ]