Question

ECMAScript 5.1, page 3:

In ECMAScript, the state and methods are carried by objects, and structure, behaviour, and state are all inherited.

What does it mean to carry state and how can an object both carry and inherit state?

Answer 1

“State” essentially refers to “things the object remembers”. If an object has a property color which is set to "blue", that’s part of its state. And “carrying state” just means that it has some.

So, we can (imprecisely) simplify the first part of that sentence to: “In ECMAScript, objects can store data (and methods).”

However, ECMAScript is an object-oriented language, using prototypical inheritance. That means any object may not only have its own data and methods, but it can also inherit data and methods from its parent object (its prototype).

Writing a very crude example in JavaScript:

function Foo() {
    this.color = "blue";
}
Foo.prototype = { shape: "circle" }

var foo = new Foo();
alert(foo.shape); // This will be "circle", even though the datum is technically part of the prototype.