跟着老师来的，效果没出来，提示length错误是怎么回事？
var WINDOW_WIDTH=1024,
WINDOW_HEIGHT=768,
RADIUS=8;
window.onload=function(){
var canvas=document.getElementById("canvas");
canvas.width=WINDOW_WIDTH;
canvas.height=WINDOW_HEIGHT;
var context=canvas.getContext("2d");
render(context);
}
function render(ctx){
var hours=12;
var minutes=34;
var seconds=56;
renderDigi(0,0,parseInt(hours/10),ctx);
}
function renderDigi(x,y,num,ctx){
ctx.fillStyle="#00f";
for(var i=0; i<digit[num].length;i++){
for(var j=0;j<digit[num][i].length;j++){
if(digit[num][i][j]==1){
ctx.beginPath();
ctx.arc(x+j*2*(RADIUS+1)+(RADIUS+1),y+i*2*(RADIUS+1)+(RADIUS+1),RADIUS,0,2*Math.PI);
ctx.closePath();
ctx.fill();
}
}
}
}
