Object-Oriented JavaScript — Inheritance and Copying Objects

Object-Oriented JavaScript — Inheritance and Copying Objects

We can copy properties and inherit properties from prototypes.

JavaScript is partly an object-oriented language.

To learn JavaScript, we got to learn the object-oriented parts of JavaScript.

In this article, we’ll look at copying objects.

Deep Copy

We can deep copy an object by copying an object’s properties recursively from the source object to the target object.

For instance, we can write:

function deepCopy(source, target = {}) {
  for (const key in source) {
    if (source.hasOwnProperty(key)) {
      if (typeof source[key] === 'object') {
        target[key] = Array.isArray(source[key]) ? [] : {};
        deepCopy(source[key], target[key]);
      } else {
        target[key] = source[key];
  return target;

We loop through each key of the source .

Then we check each property if it’s an own property.

Then we check if the source[key] object is an object.

If source[key] is an array, then we create an array, then we do the copying.

If it’s an object, then we call deepCopy recursively to make the copy.

Otherwise, we assign the value from the source to the target .

Once that’s all done, we return the target .

Then we can use it by writing:

const foo = {
  a: 1,
  b: {
    c: 2
const bar = deepCopy(foo, {});

deepCopy will copy all the own properties from foo to bar recursively.

So bar is:

  "a": 1,
  "b": {
    "c": 2

Array.isArray lets us check if something is an array regardless of context.

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