Cannot Access Object's Methods From Within Event Handler Using `this`

Below is my code for FF Extension monitoring browsing behaviour. I can't access trim method from processClick method handling click event. Console shows this.trim is not a function

Solution 1:

Use this function

Function.prototype.bind = function(obj) {   
    var _method = this;
    returnfunction() {
        return _method.apply(obj, arguments);
    };    
} 

Then,

this.registerListeners = function() {
     this.doc.addEventListener("click", this.processClick.bind(this), false);
};