Discussion

#133 Class and Prototype

byPawan KumarPawan Kumar
easy
javascript

What will be output of following code:

class User {
  constructor(name) {
    this.name = name;
  }

  greet() {
    console.log(`Hello ${this.name}`);
  }
}

console.log(typeof User);
console.log(User.prototype);
console.log(User.prototype.constructor);
console.log(Object.getOwnPropertyNames(User.prototype));

This challenge tests your knowledge about how "class" syntax actually do under the hood.

function
{
  constructor: [Function: User],
  greet: [Function: greet]
}
[Function: User]
['constructor', 'greet']

Explanation

  1. typeof User:

    • In JavaScript, classes are syntactic sugar over constructor functions, so typeof User will return `"function".

  2. User.prototype:

    • Shows an object with properties constructor and greet. The constructor property references the User function itself.

  3. User.prototype.constructor:

    • Shows the User function, indicating that the constructor property points to the User function.

  4. Object.getOwnPropertyNames(User.prototype):

    • Returns an array of the property names directly found on User.prototype, which are constructor and greet.