> For the complete documentation index, see [llms.txt](https://choubey.gitbook.io/javascript-interview-questions/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://choubey.gitbook.io/javascript-interview-questions/question-18.md).

# Question 18

### Question

How would you implement a custom `deepCopy()` method?

### Answer

Using `JSON.parse(JSON.stringify())` is a common technique for creating deep copies of objects in JavaScript. Here's a breakdown of how to implement it:

```javascript
function deepCopy(obj) {
  return JSON.parse(JSON.stringify(obj));
}
```

**Explanation:**

1. **`JSON.stringify(obj)`:** This method takes your object (`obj`) and converts it into a JSON string representation. This process essentially flattens nested objects into key-value pairs within the string.
2. **`JSON.parse(...)`:** This method then takes the JSON string and parses it back into a JavaScript object. Because of how `JSON.stringify` handles objects, this creates a completely new copy with its own references. Changes made to the copied object won't affect the original.

**Example:**

```javascript
const originalObject = {
  name: "Alice",
  age: 30,
  address: {
    street: "123 Main St",
    city: "Anytown"
  }
};

const copiedObject = deepCopy(originalObject);

copiedObject.name = "Bob"; // Change the name in the copy
console.log(originalObject); // Still outputs: { name: "Alice", age: 30, ... }


```

**Important Notes:**

* **Circular References:** `JSON.stringify()` and `JSON.parse()` will handle simple circular references (objects referencing each other). However, for complex nested cycles, you might need a more robust solution.
* **Non-Serializables:** Be mindful that not all data types are serializable by JSON. For example, functions, custom objects with non-serializable properties, or large binary data might cause issues.