creating custom visual

Hi guys. I'm trying to create a pie chart power Bi visual for practicing custom visual creation.I have followed the tutorial given in the github repo for the environment setup and now is currently on the first step , ie creating visual with static data.

The visual is being built and served correctly.But when I insert the visual in the powerBi service,all i get is a blank  screen.
Can someone help? I'm new to d3 and TypeScript, so there may be a chance that I may have made some silly mistakes.
Here's my code: 

module powerbi.extensibility.visual {
    "use strict";

    interface Data 
    {        
    quantity: number;
    category: string;
    }

    export class PieChart implements IVisual {
        private target: HTMLElement;        
        private settings: VisualSettings;
        private textNode: Text;
        private pieChartContainer:d3.Selection<SVGElement>;
        private arc:any;
        private host:IVisualHost;
        private svg:d3.Selection<SVGElement>;
        private g:any;
        private pie:any;
        private color:string;

        constructor(options: VisualConstructorOptions) {
            console.log('Visual constructor', options);
            this.target = options.element;
            this.host=options.host;
            let svg=this.svg=d3.select(options.element)
                                .append('svg')
                                .classed("pieChart",true);
            this.pieChartContainer=svg.append('g').classed('pieChartContainer',true);                        
        }


        public update(options: VisualUpdateOptions) {
            this.settings = PieChart.parseSettings(options && options.dataViews && options.dataViews[0]);
            let testData: Data[] = [
                {
                    quantity: 25,
                    category: 'a'
                },
                {
                    quantity: 50,
                    category: 'b'
                },
                {
                    quantity: 100,
                    category: 'c'
                },
                {
                    quantity: 200,
                    category: 'd'
                },
                {
                    quantity: 300,
                    category: 'e'
                }];
            let width=options.viewport.width;
            let height=options.viewport.height;
            let radius=Math.min(width,height)/2;
            this.svg.attr({
                width:width,
                height:height,
            });
            let colourValues = d3.scale.category20c();
            this.arc=d3.svg.arc()
            .innerRadius(0)
            .outerRadius(radius-20);
            this.pie = d3.layout.pie<Data>().value((d: Data):number => d.quantity);
            let fill = (d=> colourValues(d.category));
            let tf   =  d => `translate(${this.arc.centroid(d)})`;
            let text = d => d.data.category;
            this.svg.append('g')
            .attr('transform', 'translate(' + width / 2 + ',' + height / 2 + ')');
            this.g=this.svg.selectAll('.arc')
                    .data(this.pie(testData))
                    .enter()
                    .append('g')
                    .attr('class', 'arc')
                    .data(this.pie(testData));

            this.g.append('path')
                    .attr('d', this.arc)
                    .attr('fill', fill)
                    .style("stroke","black")
                    .style("stroke-width","0.8")
                    .on("mouseover",d=>
                     {
                    d3.select(d)
                    .attr('fill','blue')
                    .style('opacity','0.6')
                    .attr('d',this.arc)
                    .style("stroke","black")
                    .style("stroke-width","3");
                    this.color=d.getAttribute('fill');

                     })
                    
                    .on("mouseout",d=>
                     {   
                    d3.select(d)
                    .attr('fill',colourValues(this.color))
                    .style("opacity","1")
                    .attr('d',this.arc)
                    .style("stroke-width","0.8");
                    }).append("svg:title");
                    //.html(d=>'<p>Quantity :'+d=>d. + '</p>');           
                    this.g.append('text').attr('transform', tf).text(text);
        }


        private static parseSettings(dataView: DataView): VisualSettings {
            return VisualSettings.parse(dataView) as VisualSettings;
        }

        /** 
         * This function gets called for each of the objects defined in the capabilities files and allows you to select which of the 
         * objects and properties you want to expose to the users in the property pane.
         * 
         */
        public enumerateObjectInstances(options: EnumerateVisualObjectInstancesOptions): VisualObjectInstance[] | VisualObjectInstanceEnumerationObject {
            return VisualSettings.enumerateObjectInstances(this.settings || VisualSettings.getDefault(), options);
        }
    }
}