Defining JavaScript functions inside vs. outside of a class

From the MDN doc:

JavaScript classes, introduced in ECMAScript 2015, are primarily syntactical sugar over JavaScript's existing prototype-based inheritance. The class syntax does not introduce a new object-oriented inheritance model to JavaScript.

So this...

class TestClass {
  constructor(myName) {
    this.name = myName;
  }

  getName() {
    return this.name;
  }

  static getName2() {
    return 'getName2 result';
  }
}

...is exactly equivalent to this:

const TestClass = function(myName) {
  this.name = myName;
}

TestClass.prototype.getName = function() {
  return this.name;
}

TestClass.getName2 = function() {
  return 'getName2 result';
}

---

So whether you use the older prototype syntax or the newer ES6 class syntax is just a matter of personal preference, and as you suspected, defining methods directly on a class is exactly equivalent to creating a static class method.