i am trying to learn frontend development from a book called Front-end Web Development : Big Nerd Ranch Guide , I am copy/pasting code book into my computer but today i got a error that one of my function’s is not constructor, this section of the book describe how to use jQuery and how to build and connect different module’s in ES5 using some coding technique which i will copy here, here is the function module that will give the error called formhandler.js :

(function (window) {
    'use strict'
    var App = window.App || {};
    var $ = window.jQuery;

    function FormHandler(selector) {
        if (!selector) {
            throw new Error('No selector provided');
        }
        this.$formElement = $(selector);
        if (this.$formElement.length === 0) {
            throw new Error('Could not find element with selector:' + selector);
        }
    }
    FormHandler.prototype.addSubmitHandler = function (fn) {
        console.log('Setting submit handler for form');
        this.$formElement.on('submit', function (event) {
            event.preventDefault();
            var data = {};
            $(this).serializeArray().forEach(function (item) {
                data[item.name] = item.value
                console.log(item.name + ' is ' + item.value);
            })
            console.log(data);
            fn(data);
            
        });
    };

    App.FormHandler = FormHandler;
    window.App = App;
}
)(window);

and this is main.js which call’s and connect the module’s :

(function (window) {
    'use strict';
    var FORM_SELECTOR = '[data-coffee-order="form"]';
    var App = window.App;
    var Truck = App.Truck;
    var DataStore = App.DataStore;
    var FormHandler = App.FormHandler;
    var myTruck = new Truck('ncc-1701',new DataStore());
    window.myTruck = myTruck;
    var formHandler = new FormHandler(FORM_SELECTOR);

    formHandler.addSubmitHandler(myTruck.createOrder.bind(myTruck));
    console.log(formHandler);
})(window);

the statement var formHandler = new FormHandler(FORM_SELECTOR); gives typeError : FormHandler is not a constructor , which from first module and the book it is suppose to be.

I suspected that I am assigning FormHandler to something other than it’s main method but that seems not and also since this is copy paste from the book its hard for me to find another cause of the error.
Thanks