What is ES6 class? How does it differ from function constructors?

ES6 Class Syntax

ES6 introduced the class keyword for a cleaner object-oriented syntax.

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

  speak() {
    console.log(this.name + ' makes a sound.');
  }
}

class Dog extends Animal {
  speak() {
    console.log(this.name + ' barks.');
  }
}

const d = new Dog('Rex');
d.speak(); // 'Rex barks.'

Function Constructor (ES5)

function Animal(name) {
  this.name = name;
}

Animal.prototype.speak = function() {
  console.log(this.name + ' makes a sound.');
};

function Dog(name) {
  Animal.call(this, name);
}

Dog.prototype = Object.create(Animal.prototype);
Dog.prototype.constructor = Dog;

Dog.prototype.speak = function() {
  console.log(this.name + ' barks.');
};

Key Differences

Feature	Class	Function Constructor
Syntax	Clean and concise	Verbose
Hoisting	Not hoisted (TDZ)	Hoisted (function declarations)
Strict mode	Enabled by default	Must add manually
Requires new	Enforced (TypeError without it)	Silently fails without new
Inheritance	extends + super	Manual prototype setup
Static methods	static keyword	Attach directly to the function

Under the Hood

ES6 class is syntactic sugar — the underlying mechanism is still prototype-based inheritance.

typeof class Foo {} // 'function'