ES6 Classes - Calling methods from a click event

Question

I am new to ECMA classes.

In the following code, I have built a button class that is working fine. Now I am trying to call the prev_image() method from inside the click eventlistener. I know 'this' refers to the button instance but am not sure how to call a method from the Gallery class. Thanks for any help.

class Gallery{

    constructor(){
    }

    draw(){

        //build button
        prevbtn.draw();

        //button listener
        document.getElementById('prevbtn').addEventListener('click', function(){
            this.prev_image();   <--- this errors out
            console.log('pressed'); <--this works
        });

    }

    prev_image(){
        console.log('previous image!');
    }

}

Solution 1

document.getElementById('prevbtn').addEventListener('click', ()=>{
            this.prev_image();   
            console.log('pressed');
        });

Use the arrow function here.Arrow function does not have its own this it uses this from the code that contains the Arrow Function

Solution 2

Try it by binding the context using .bind(this)

class Gallery {

  constructor() {}

  draw() {

    //build button
    //prevbtn.draw();

    //button listener
    document.getElementById('prevbtn').addEventListener('click', function() {
      this.prev_image();
      console.log('pressed');
    }.bind(this));

  }
  // prevbtn.draw(){
  //console.log('prev btn')
  //}

  prev_image() {
    console.log('previous image!');
  }

}

var x = new Gallery();
x.draw();

<button id='prevbtn'>Click</button>

Comments

[Bergi]

Every function does lexical scoping. I guess you don't mean variable "scope"?

[Saikat Hajra]

exactly not the variable scope. I would rather add few more lines to explain :) @Bergi

[Bergi]

So please edit your answer and don't use the term "scope".