I am having tough time understanding the meaning of Instance properties
For example in Firefox ES6 Class document it says https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes
Instance properties
Instance properties must be defined inside of class methods
class Rectangle {
constructor(height, width) {
this.height = height;
this.width = width;
}
}
I just see this as a class with constructor, so what do they mean by instance properties?
The instance properties there are height and width:
class Rectangle {
constructor(height, width) {
this.height = height;
// -----^^^^^^
this.width = width;
// -----^^^^^
}
}
An "instance" is an object. One tends to use "instance" in relation to code using class-like syntax, but it just means object (though often the implication is "object of a particular class").
Contrast with "static" or "class" properties:
class Rectangle {
constructor(height, width) {
this.height = height;
this.width = width;
}
}
Rectangle.FOUR_BY_FOUR = new Rectangle(4,4);
There, FOUR_BY_FOUR is a "class/static" property. Or using the syntax proposed by the static class features proposal (currently Stage 3):
class Rectangle {
static FOUR_BY_FOUR = new Rectangle(4,4);
constructor(height, width) {
this.height = height;
this.width = width;
}
}
That means each instance of a Rectangle will have the properties height and width.
Later, they show how to create an instance.
const square = new Rectangle(10, 10);
Here, square is an instance of a Rectangle whose height and width properties are both initialized to 10.
You can picture class as a blueprint or modelling. Using the class that you've defined in your question for explanation
class Rectangle {
constructor(height, width) {
this.height = height;
this.width = width;
}
}
We have a class named Rectangle as a "blueprint" or design. Now we can create many individual instance/object by defining their own instance properties, base on this "blueprint"/Rectangle
let bigRectangle = new Rectangle(300,300);
let smallRectangle = new Rectangle(50,50);
person, then you want thenameproperty of that to hold a different value for each person instance you create … Opposed to that would be a static property, one that all instances share.