var oldPosition = {'x':100,'y':100};//图形的起始点
var area = {'w' : 50 , 'h' : 50};//绘制图形的宽高
var cvs = document.getElementById('cvs');
drawing : function(){
var ctx = this.canvas.getContext('2d');//得到画笔
ctx.clearRect(0,0,this.canvas.width,this.canvas.height);//每次绘制前先清除之前绘制的图形
ctx.beginPath();
ctx.fillStyle = this.color;
ctx.fillRect(this.oldPosition.x,this.oldPosition.y,this.area.w,this.area.h);
ctx.closePath();
}