Earlier quoted context omitted.
You don't have to bind 'method' in the constructor to access 'y'. Just put 'this.y = 10;' in the constructor. Your example isn't legal JavaScript.
It's perfectly legal Javascript. Why would I put this.y = 10 in the cinstructor? Do you even understand what this code does? const instance = new C(); for(let i = 0; i If you don't bind `this` to `method` in the constructor, when you call `instance.method()`, `this` will be whatever (window, IIRC). Don't believe me? Try a more complex example like React's event handling with `this.setState()`: https://reactjs.org/doc…
Now onto bound methods: you are wrong in your code example; `instance.method()` does not require `method` to be a bound method; an unbound function is just fine. The code is equivalent to `instance.method.call(instance)`, which (for an unbound function) calls it with `instance` as its context. The problem is when, at call time, you don’t access the function as a property on another object, like this:
const fn = instance.method;
fn();
Bound methods are created by Function.prototype.bind, or by arrow functions.
In what I will choose to call “normal code”, it’s somewhere between very rare and not particularly common to need to bind a function manually. Understand this: React is not normal code. React was designed in a distinctly unusual way (they invented an rather substantial language extension to achieve it!), and although that language and design has turned out quite well in most ways, it also has some exceptionally nasty weaknesses and rather annoying ergonomic troubles; and the need to bind functions is one of them. This is not JavaScript’s fault, but is because React has gone for a VDOM approach that (I think?) requires object identity in such cases, for reasons of efficiency. In search of one form of ergonomics, they damaged another form that others don’t have to worry about very often at all. Such is life, and the nature of tradeoffs.
Most of the trouble with needing bound functions happens with event handling. (Certainly not all, but most, in my experience.) In non-React, non-VDOM-based code, you might be doing something like this:
const foo = document.createElement('foo');
foo.addEventListener('bar', event => {
…
});
Sometimes you would want a separate function to designate the event handler, and so you may want to call bind(), but it’s also just as likely that you’ll want to keep Event out of that method, and just do `foo.addEventListener('bar', event => this.handleBar(event.detail))`. Maybe, maybe not.
From your earlier example: be careful with your `x = () => …` instead of `x() { … }`, because that instantiates a new function for every instance of the object, which is very inefficient for memory consumption and performance. Binding a method from the prototype is much more efficient (though still to be avoided where unnecessary).
The most interesting approach to resolving this binding problem that React causes lies in the decorators proposal (currently at stage 2). https://github.com/tc39/proposal-decorators/blob/master/boun... is all about a @bound decorator.
* Just be careful with adding event listeners, and remember to use bubbling.