is javascript now support classes or not and why i feel no stability?

JavaScript classes introduced in ECMAScript 2015 are addition to JavaScript's existing prototype-based inheritance. JavaScript classes provide a much simpler and clearer syntax to create objects and deal with inheritance, however the class syntax is not introducing a new object-oriented inheritance model to JavaScript.

One way to define a class is using a class declaration. To declare a class, you use the class keyword with the name of the class ("Car" for example):

class Car{
  constructor(weight, year) {
    this.weight= weight;
    this.year= year;
  }
}

You first need to declare your class and then access it (unlike declaration of function), otherwise you will get a ReferenceError.

In JavaScript, as of ECMA-Script 2015 and above, there's a new and fancy class syntax, but it's all about a syntactic sugar layer on top of prototype chain.

See this code sample:

// ECMA-Script 2015 and above
class A {
}
class B extends A {
}
// ECMA-Script 5 or what's really happening behind the scenes:
function A() {}
function B() {}
B.prototype = Object.create(A.prototype);

Are classes in JavaScript? From a high level point of view, yes, they're. But it's not a type system like you would find in other programming languages like C++, C#, Java, Ruby, Python...

Further reading

• How does JavaScript .prototype work?