用html5绘制折线图的实例代码

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 html  canvas id= a_canvas width= 1000 height= 700 /canvas  script  (function (){  window.addEventListener( load , function(){  var data = [100,-1000,0,700];  // 获取上下文  var a_canvas = document.getElementById( a_canvas  var context = a_canvas.getContext( 2d  // 绘制背景  var gradient = context.createLinearGradient(0,0,0,300);  // gradient.addColorStop(0, #e0e0e0  //gradient.addColorStop(1, #ffffff  context.fillStyle = gradient;  context.fillRect(0,0,a_canvas.width,a_canvas.height);  // 描绘边框  var grid_cols = data.length + 1;  var grid_rows = 4;  var cell_height = a_canvas.height / grid_rows;  var cell_width = a_canvas.width / grid_cols;  context.lineWidth = 1;  context.strokeStyle = #a0a0a0  // 结束边框描绘  context.beginPath();  // 准备画横线  /*for (var col = 0; col = grid_cols; col++) {  var x = col * cell_width;  context.moveTo(x,0);  context.lineTo(x,a_canvas.height);  // 准备画竖线  for(var row = 0; row = grid_rows; row++){  var y = row * cell_height;  context.moveTo(0,y);  context.lineTo(a_canvas.width, y);  }*/  //划横线  context.moveTo(0,a_canvas.height/2);  context.lineTo(a_canvas.width,a_canvas.height/2);  //画竖线  context.moveTo(0,0);  context.lineTo(0,a_canvas.height);  context.lineWidth = 1;  context.strokeStyle = #c0c0c0  context.stroke();  var max_v =0;  for(var i = 0; i data.length; i++){  var d=0;  if(data[i] 0)  {dd=d-data[i];  else{d=data[i];};  if (d max_v) { max_v =d};  max_vmax_v = max_v * 1.1;  // 将数据换算为坐标  var points = [];  for( var i=0; i data.length; i++){  var v= data[i];  var px = cell_width * (i +1);  var py = a_canvas.height/2 - a_canvas.height*(v / max_v)/2;  points.push({ x :px, y :py});  // 绘制折现  context.beginPath();  context.moveTo(points[0].x, points[0].y);  for(var i= 1; i points.length; i++){  context.lineTo(points[i].x,points[i].y);  context.lineWidth = 2;  context.strokeStyle = #8BA9FF  context.stroke();  //绘制坐标图形  for(var i in points){  var p = points[i];  context.beginPath();  context.arc(p.x,p.y,4,0,2*Math.PI);  //实心圆  context.fillStyle = #000 */  //空心圆  context.strokeStyle = #000  context.stroke();  context.fill >
运行结果如下：
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