JavaScript

How to use Class in JS (1)

Class, JavaScript

(This is my personal practice on this page. May use some similar codes.)

Declare a class

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class Page {
  constructor(words, lines){
    this.words = words;
    this.lines = lines;
  }
}

This code declares a class Page, with two inputs for its members.

Important: Classes are NOT hoisted, oppose to methods.

Class body and method definitions

  • Strict Mode is used for class definitions and class expressions.
  • Constructor can be used for creating and initializing instances.

  • Prototype methods

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    class Page {
      constructor(words, lines){
        this.words = words;
        this.lines = lines;
      }
      // let's pretend this is real lol
      get wordCount(){
        return this.calcCount();
      }
      calcCount() {
        return this.words * this.lines;
      }
    }
    const page = new Page(25, 20);
    console.log(page.wordCount);

  • Static methods
    The word static defined static method. They are called without instantiating class and CANNOT be called through class instance.

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    class Point {
      constructor(x,y){
        this.x = x;
        this.y = y;
      }
      static distance(a,b){
        const dx = a.x - b.x;
        const dy = a.y - b.y;
        return Math.sqrt(dx*dx + dy*dy);
      }
    }
    const p1 = new Point(5,5);
    const p2 = new Point(10,10);
    console.log(Point.distance(p1,p2));
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