javascript - Accessing instance variables from other functions

I can't access a JavaScript variable from another function that has been instantiated in the constructor function. It returns undefined.

I am instantiating a new object of the class Box, and in the constructor function, defining instance variables, creating HTML elements and setting up an event listener. The handler for this listener, clickHandler, is a function that is defined on the prototype. From clickHandler, I am trying to access the this.selected variable. But I get undefined.

The code:

HTML

Javascript script.js

function Box(id, count) { //the class
    this.selected = false; //need this variable in clickHandler
    this.div = document.createElement("div");
    this.div.id = "container" + count;

    this.div.style.width = "250px";
    this.div.style.height = "150px";
    this.div.style.border = "1px solid black";
    document.getElementById(id).appendChild(this.div);
    this.div.addEventListener("click", this.clickHandler, false); //add event listener on the created div element
}

Box.prototype.clickHandler = function() { //click handler
    console.log("clickHandler, selected = " + this.selected); // undefined
};


function init(settings) {
    //var obj;
    for(var i = 0; i < settings.length; i++) {
        new Box(settings[i].id, (i+1)); //instantiate new object
    }
}

How can I access the this.selected variable in various event handler functions? I plan to listen for multiple events and need the this.selected variable for that. Thank you for the help.