learnjavascript

160 readers
1 users here now

  1. Be Welcoming. n00bs are welcome here. Negativity is not.

  2. Include Context If you’re asking for help, include enough information for others to recreate your problem.

  3. No unvetted self promotion Message the mods first.

founded 4 years ago
MODERATORS
1
 
 

How ChatGPT Can Be Your JavaScript Coding Buddy

2
 
 

I have been reading this book "Modern Javascript for the Impatient", chapter "Object-Oriented Programming". At the end there is an "Exercise" section. This is a question from it I need help answering:


Harry tries this code to toggle a CSS class when a button is clicked:

const button = document.getElementById('button1')
button.addEventListener('click', function () {
  this.classList.toggle('clicked')
})

It doesn’t work. Why?

Sally, after searching the wisdom of the Internet, suggests:

button.addEventListener('click', event => {
  event.target.classList.toggle('clicked')
})

This works, but Harry feels it is cheating a bit. What if the listener hadn’t produced the button as event.target? Fix the code so that you use neither this nor the event parameter.


3
 
 

I have been reading a book on JS. This is one of the questions at the end of a chapter that stumped me; don't know where to begin. So please help me out:

Question

A classic example for an abstract class is a tree node. There are two kinds of nodes: those with children (parents) and those without (leaves).

class Node {
  depth() { throw Error("abstract method") }
}
class Parent extends Node {
  constructor(value, children) { . . . }
  depth() { return 1 + Math.max(...children.map(n => n.depth())) }
}
class Leaf extends Node {
  constructor(value) { . . . }
  depth() { return 1 }
}

This is how you would model tree nodes in Java or C++. But in JavaScript, you don’t need an abstract class to be able to invoke n.depth().

Rewrite the classes without inheritance and provide a test program.

So, how to write this code without using inheritance in JS?

4
5