画布在javascript中为空错误
我有以下代码:画布在javascript中为空错误,javascript,html,canvas,Javascript,Html,Canvas,我有以下代码: <!DOCTYPE html> <html> <head> <style type="text/css"> canvas{border:#666 1px solid;} </style> <script type="text/javascript"> var canvas = document.getElementById("canvas"), context = canvas.get
<!DOCTYPE html>
<html>
<head>
<style type="text/css">
canvas{border:#666 1px solid;}
</style>
<script type="text/javascript">
var canvas = document.getElementById("canvas"),
context = canvas.getContext("2d"),
playerimage = new Image(),
x = canvas.width / 2, //align to centre of the screen
y = canvas.height / 2, //same as above
speed = 5, //speed for the player to move at
width = 50, //width of the player
height = 50; //height of the player
function init() {
playerimage.src = "ninja.png"; //path to the image to use for the player
canvas.addEventListener("keypress", update);
}
function update(event) {
if (event.keyCode == 38) {
y -= speed; //going up
}
if (event.keyCode == 40) {
y += speed; //going down
}
if (event.keyCode == 37) {
x -= speed; //going left
}
if (event.keyCode == 39) {
x += speed; //going right
}
render();
}
function render() {
// context.clearRect(0, 0, canvas.width, canvas.height);
context.drawImage(playerimage, x, y, width, height);
}
</script>
</head>
<body onload="init();">
<button onclick="init();">Draw</button>
<canvas id="Mycanvas" width="550" height="400"></canvas>
</body>
</html>
画布{边框:#666 1px实心;}
var canvas=document.getElementById(“canvas”),
context=canvas.getContext(“2d”),
playerimage=新图像(),
x=canvas.width/2,//与屏幕中心对齐
y=canvas.height/2,//同上
速度=5,//玩家移动的速度
宽度=50,//播放器的宽度
高度=50//运动员身高
函数init(){
playerimage.src=“ninja.png”;//用于播放器的图像的路径
canvas.addEventListener(“按键”,更新);
}
功能更新(事件){
如果(event.keyCode==38){
y-=速度;//上升
}
如果(event.keyCode==40){
y+=速度;//下降
}
如果(event.keyCode==37){
x-=速度;//向左转
}
如果(event.keyCode==39){
x+=速度;//向右转
}
render();
}
函数render(){
//clearRect(0,0,canvas.width,canvas.height);
drawImage(playerimage,x,y,宽度,高度);
}
画
javascript控制台总是给我画布为空错误以下代码行存在两个问题:
var canvas = document.getElementById("canvas"),
var canvas = document.getElementById("Mycanvas"),
…并将整个
块移动到正文的末尾,就在
之前,html中画布的id与中使用的id不匹配
var canvas=document.getElementById("canvas");
正确的HTML应该是:
<canvas id="canvas" width="550" height="400"></canvas>
顺便说一句,用分号(;
)代替逗号(,
)来分隔javascript中的命令。@PetrR.-不是在声明多个变量的多行var
语句中。@nnnnnn-我没有意识到这一点。我的错。