How to add click alert on each box using Javascript function constructor?

Question

Html code:

    <div class="box green">I'm green!</div>
    <div class="box blue">I'm blue!</div>
    <div class="box orange">I'm orange!</div>

CSS code here:

    .green { background-color: green; }
    .blue { background-color: dodgerblue; }
    .orange { background-color: orangered; }

JavaScript code here using object literal syntax : // want to apply same effect to box2 and box3

var box1 = {
color: 'Green',
number: 1,
clickMe: function () {
    var green = document.querySelector('.green');
    var self = this;

    green.addEventListener('click', function () {

        var str = 'This is box number ' + self.number + ' and it is ' + self.color;

        alert(str);

    });

  }
}

box1.clickMe();

Answer 1

If you wish to use a constructor you can use a class. You can use a constructor like so (see snippet), where it accepts a color and a number.

You then need to modify your function within the addEventListener to be an arrow function (() => {}) so it references the correct this when called.

Lastly, when creating your boxes you need to provide a color and a number as defined by the constructor (var myBox = new Box(COLOR, NUMBER)):

class Box {
  constructor(color, number) {
    this.color = color;
    this.number = number;
  }

  clickMe() {
    var elem = document.querySelector('.' + this.color);
    elem.addEventListener('click', () => {
      var str = 'This is box number ' + this.number + ' and it is ' + this.color;
      alert(str);
    });
  }
}


var box1 = new Box('green', 1);
var box2 = new Box('blue', 2);
var box3 = new Box('orange', 3);

box1.clickMe();
box2.clickMe();
box3.clickMe();

.green { background-color: green; }
.blue { background-color: dodgerblue; }
.orange { background-color: orangered; }

<div class="box green">I'm green!</div>
<div class="box blue">I'm blue!</div>
<div class="box orange">I'm orange!</div>

Answer 2

You can pass parameters in clickMe function and use that in alert box:

var box1 = {
clickMe: function (color, number) {
    var box = document.querySelector('.'+color);

    box.addEventListener('click', function () {

        var str = 'This is box number ' + number + ' and it is ' + color;

        alert(str);

    });

  }
}

box1.clickMe('green', 1);
box1.clickMe('blue', 2);
box1.clickMe('orange', 3);

.green { background-color: green; }
.blue { background-color: dodgerblue; }
.orange { background-color: orangered; }

<div class="box green">I'm green!</div>
<div class="box blue">I'm blue!</div>
<div class="box orange">I'm orange!</div>

Answer 3

You could iterate over elements (and add event listeners once) using a for and access to this with arrow functions (()=>{}), like this:

var box = {
  color: ['Green', 'Blue', 'Orange'],
  number: [1, 2, 3],
  clickMe: function() {
    var colors = document.getElementsByClassName('box');

    for (let i = 0; i < colors.length; i++) {

      colors[i].addEventListener('click', () => {

        var str = 'This is box number ' + this.number[i] + ' and it is ' + this.color[i];

        alert(str);

      });
    }
  }

Here a full example https://jsfiddle.net/25uLvstp/

In this way, you could define all boxes listeners at once.