Drawing Rectangle with mouse

HTML

<script src="https://rawgithub.com/kangax/fabric.js/master/dist/fabric.js"></script>
<canvas id="canvas" style="border: 2px solid darkblue"></canvas>
<div style="position: relative; width: 1300px; height:30px; border: 2px solid black; margin-top: 5px">
    <input type="button" id="selDiv" value="Container">
</div>

JavaScript

//Start when the document is loaded
        $(document).ready(function () {
            //Create variable to track ability to draw
            var canDraw = true;

            //Getting the canvas
            var canvas1 = new fabric.Canvas('canvas');
            //Setting the canvas properties
            canvas1.setHeight(600);
            canvas1.setWidth(800);
            canvas1.renderAll();
            // canvas1.selection = false;
            //End of canvas1

            var grid = 50;
            // create grid
            for (var i = 0; i < (800 / grid); i++) {
                canvas1.add(new fabric.Line([i * grid, 0, i * grid, 800], {
                    stroke: '#ccc',
                    selectable: false
                }));
                canvas1.add(new fabric.Line([0, i * grid, 800, i * grid], {
                    stroke: '#ccc',
                    selectable: false
                }));
            }
            // snap to grid
            /*   canvas1.on('object:moving', function (options) {
                options.target.set({
                    left: Math.round(options.target.left / grid) * grid,
                    top: Math.round(options.target.top / grid) * grid
                });
            });*/

            //Create DivContainer Class
            fabric.DivContainer = fabric.util.createClass(fabric.Rect, {

                //type for consistency
                type: 'div-container',

                //constructor
                initialize: function (options) {
                    options || (options = {});

                    //call super constructor for render abilities
                    this.callSuper('initialize', options);
                    this.set('hasRotatingPoint', false);
                    this.set('borderOpacityWhenMoving', 1);
                    this.set('borderColor', '#1FFFC7');
                    this.set('cornerColor', '#1FFFC7');
                    this.set('x', options.x || 0);
                   ...