Great question—this is one of the most common "wait, that contradicts itself!" moments for people learning JavaScript, especially if you’re coming from a class-based language like Java or C++. Let’s break this down clearly:

First, the context of that older statement #

The line you found in the "Custom Objects" section refers to pre-ES6 JavaScript (before 2015). Back then, JavaScript truly had no class keyword at all. It’s a prototype-based language, so all object-oriented behavior was built using function constructors and prototype chains, like this:

// Pre-ES6 "class" using a function constructor
function Car(make, model) {
  this.make = make;
  this.model = model;
}
// Add methods to the prototype
Car.prototype.drive = function() {
  console.log(`Driving my ${this.make} ${this.model}`);
};

This is why the document says "contains no class statement"—that was 100% true before ES6 rolled out.

The class keyword is syntactic sugar, not a true "class" system #

When ES6 launched in 2015, it introduced the class keyword to make JavaScript’s object-oriented code look more familiar to developers used to traditional OOP languages. But here’s the key: it’s just a nicer way to write the same prototype-based code under the hood.

Take the ES6 version of the Car example:

class Car {
  constructor(make, model) {
    this.make = make;
    this.model = model;
  }
  drive() {
    console.log(`Driving my ${this.make} ${this.model}`);
  }
}

If you inspect this code in a browser’s developer tools, you’ll see that the Car class is still a function, and the drive method is still attached to Car.prototype. It doesn’t change JavaScript’s core prototype-based nature—it just hides the prototype boilerplate.

Why MDN mentions both #

MDN’s documentation has evolved over time:

• The older "Custom Objects" section was written before ES6, and while it might not have been fully updated, it’s emphasizing JavaScript’s fundamental nature (it’s still prototype-based at heart).
• The newer "Classes" section covers the modern class syntax because it’s now a standard part of the language, even if it’s syntactic sugar.

You didn’t miss anything, and the content isn’t fully "outdated"—it’s just highlighting two layers of JavaScript: the underlying prototype system, and the modern syntax that makes it easier to work with.

内容的提问来源于stack exchange，提问作者meJustAndrew