Trying to create a class in JS with the attribute weight in the following code:
function Foo() {
var weight = 10;
console.log(weight);
}
When I instantiate it with var bar = new Foo();, 10 is logged to the console.
When I later call console.log(bar.weight);, undefined is logged to the console. Why is that? I was under the impression that the attributes declared within a JS class were public by default?
That's because you haven't actually set weight as a property of bar; it's merely a local variable created upon the constructor call (this differs from some other languages, like Java, for example). To create it as a property, you need to use the keyword this:
function Foo() {
this.weight = 10;
}
That sets weight to be a property of Foo objects, including bar, so you should be able to use console.log(bar.weight) without issue.
function Foo() {
this.weight = 10;
}
var bar = new Foo();
document.body.innerHTML = "<code>bar</code>'s weight property is equal to " + bar.weight + ".";
Because weight is not property of Food but a local variable, Change
var weight = 10;
to
this.weight = 10;
this.weightexplicitly.varalways declares a variable in that scope, no matter how or where a function is called.