JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
    <form action="" method="post" id="input">
            <input type="submit">
    </form>
</div>

JavaScript

$(function() {
    $("#container").css("background", "red");
    var ReserveUI = function($el) {
        this.$form = {
            input: $el.find('#input')
        };
        this._eventify();
    };
    
    ReserveUI.prototype.doSomething = function() {
        return false;
    }
        
    ReserveUI.prototype._eventify = function() {
        this.$form.input.submit(function() {
            this.doSomething(); //if comment out this line, it works
            return false;
        });
    };
    var UI = new ReserveUI($("#container"));
});