How to span a variable to a class in javascript
I am trying to create a class using the foo {} class syntax and want a private variable inside it. Right now I have something like this:
'use strict';
class foo {
constructor(x1,y1) {
var x = x1;
var y = y1;
}
get x() {
return x;
}
get y() {
return y;
}
}
Whenever I try to access the files foo.x and foo.y, I get x not found error. However, when I tried to put variable declarations outside of the constructor, it stopped working. I also use static methods, so I can't get away with the class syntax without doing some work. How can I fix this? How can I declare a variable inside an object that is global and cannot be found outside?
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These getters are declared on the prototype where they cannot access the private (copied) variables in the constructor. You will need to use Object.defineProperty
to create instances specific to instances:
class Foo {
constructor(x, y) {
Object.defineProperties(this, {
x: {get() { return x; }, configurable: true},
y: {get() { return y; }, configurable: true}
});
}
}
This is no different from ES5. Btw if you don't assign variables you can also make them unwritable properties.
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Okay, people are assuming you want to use getters and setters. If it doesn't, this will be enough:
'use strict';
class foo {
constructor(x1,y1) {
this.x = x1;
this.y = y1;
}
}
var f = new foo(10, 20);
console.log(f.x)
console.log(f.y)
JSFiddle: https://jsfiddle.net/gLxnqfrv/
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Taken from es6-features , this is the correct syntax for the class as well as its getters and setters.
class Rectangle {
constructor (width, height) {
this._width = width
this._height = height
}
set width (width) { this._width = width }
get width () { return this._width }
set height (height) { this._height = height }
get height () { return this._height }
get area () { return this._width * this._height }
}
var r = new Rectangle(50, 20)
r.area === 1000
It's important to note that there is no prototype damage requirement in ES6.
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