JavaScript: Create a new object from the combination of two or more objects

JavaScript fundamental (ES6 Syntax): Exercise-178 with Solution

Merge Objects into New Object

Write a JavaScript program to create a new object from the combination of two or more objects.

• Use Array.prototype.reduce() combined with Object.keys() to iterate over all objects and keys.
• Use Object.prototype.hasOwnProperty() and Array.prototype.concat() to append values for keys existing in multiple objects.

Sample Solution:

JavaScript Code:

// Define a function 'merge' that takes any number of objects as arguments using the rest parameter syntax '...objs'
const merge = (...objs) =>
  // Use the spread operator to create a shallow copy of the 'objs' array, then use 'reduce' to merge the objects
  [...objs].reduce(
    // Callback function for 'reduce' with accumulator 'acc' and current object 'obj'
    (acc, obj) =>
      // Reduce the keys of the current object 'obj' into the accumulator 'acc' using another 'reduce' function
      Object.keys(obj).reduce(
        // Callback function for inner 'reduce' with accumulator 'a' and current key 'k'
        (a, k) => {
          // Check if the accumulator 'acc' already has the key 'k'
          acc[k] = acc.hasOwnProperty(k) ? // If yes, concatenate the values of 'acc[k]' and 'obj[k]' arrays or add the value 'obj[k]' to 'acc[k]'
            [].concat(acc[k]).concat(obj[k]) : obj[k];
          return acc; // Return the updated accumulator 'acc'
        },
        {} // Initial value of the inner 'reduce' accumulator is an empty object
      ),
    {} // Initial value of the outer 'reduce' accumulator is an empty object
  );

// Define two objects 'object' and 'other' with properties 'a', 'b', and 'c'
const object = {
  a: [{ x: 2 }, { y: 4 }],
  b: 1
};
const other = {
  a: { z: 3 },
  b: [2, 3],
  c: 'foo'
};
// Merge the two objects using the 'merge' function and log the result
console.log(merge(object, other));

Output:

{"a":[{"x":2},{"y":4},{"z":3}],"b":[1,2,3],"c":"foo"}

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-178-1 by w3resource (@w3resource) on CodePen.

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