js代码引用要在canvas标签下面

document.body.onload = game;

function game(){

//初始工作

init();

}

function init(){

//获得canvas、context

var can1 = document.getElementById("canvas1");//在前面：fishes、UI、dust、circle

var ctx1 = can1.getContext();

var can2 = document.getElementById("canvas2");//background、ane、fruits

var ctx2 = can2.getContext();

}

function gameloop(){

requestAnimFrame(gameloop);

}