//餅圖顯示
<p>  
   <canvas id="canvas_circle" width="290" height="200"> </canvas>  
</p>


//繪製
<script>  
            //繪製餅圖  
            function drawCircle(canvasId, data_arr, color_arr, text_arr)  
            {  
                var c = document.getElementById(canvasId);  
                var ctx = c.getContext("2d");  
  
                var radius = c.height / 2 - 20; //半徑  
                var ox = radius + 20, oy = radius + 20; //圓心  
  
                var width = 30, height = 10; //圖例寬和高  
                var posX = ox * 2 + 20, posY = 30;   //  
                var textX = posX + width + 5, textY = posY + 10;  
  
                var startAngle = 0; //起始弧度  
                var endAngle = 0;   //結束弧度  
                for (var i = 0; i < data_arr.length; i++)  
                {  
                    //繪製餅圖  
                    endAngle = endAngle + data_arr[i] * Math.PI * 2; //結束弧度  
                    ctx.fillStyle = color_arr[i];  
                    ctx.beginPath();  
                    ctx.moveTo(ox, oy); //移動到到圓心  
                    ctx.arc(ox, oy, radius, startAngle, endAngle, false);  
                    ctx.closePath();  
                    ctx.fill();  
                    startAngle = endAngle; //設定起始弧度  
  
                    //繪製比例圖及文字  
                    ctx.fillStyle = color_arr[i];  
                    ctx.fillRect(posX, posY + 20 * i, width, height);  
                    ctx.moveTo(posX, posY + 20 * i);  
                    ctx.font = 'bold 12px 微軟雅黑';    //斜體 30畫素 微軟雅黑字型  
                    ctx.fillStyle = color_arr[i]; //"#000000";  
                    var percent = text_arr[i] + "：" + 100 * data_arr[i] + "%";  
                    ctx.fillText(percent, textX, textY + 20 * i);  
                }  
            }  
  
            function init() {  
                //繪製餅圖  
                //比例資料和顏色  
                var data_arr = [0.1,0.2, 0.3, 0.4];  
                var color_arr = ["BLUE",'RED','YELLOW','GREEN'];  
                var text_arr = ["第一季度", "第二季度", "第三季度", "第四季度"];  
  
                drawCircle("canvas_circle", data_arr, color_arr, text_arr);  
            }  
  
            //頁面載入時執行init()函式  
            window.onload = init;  
        </script>