Which object copying methods can copy functions from one object to another?

In JavaScript, functions are first-class objects and can be copied along with objects in various ways. Here are the main methods of copying an object that preserve functions:

1. Object.assign() — copies all enumerable own properties, including functions.

const obj = {
  a: 1,
  fn() { return this.a; }
};
const copy = Object.assign({}, obj);
console.log(copy.fn()); // 1

2. Spread operator {...obj} — also copies functions, as they are properties of the object.

const copy2 = {...obj};
console.log(copy2.fn()); // 1

3. JSON.stringify + JSON.parse — does not copy functions, as JSON does not support functions.

4. Manual copying of properties, including functions.

Thus, copying methods based on shallow copying of object properties (Object.assign, spread) preserve functions, while JSON serialization does not.