document.getElementByClassName找不到Javascript内部类
我正在制作一个物理引擎,它利用JavaScript来创建具有物理属性的框,这些属性按窗口大小的比例应用于它们。但是,函数document.getElementByClassName找不到Javascript内部类,javascript,getelementsbyclassname,Javascript,Getelementsbyclassname,我正在制作一个物理引擎,它利用JavaScript来创建具有物理属性的框,这些属性按窗口大小的比例应用于它们。但是,函数document.getElementByClassName(“box”)找不到包含这些框的所有物理属性的名为box的类 我试图分配一个变量boxelem,以包含每个单独框的位置属性,以便将来可以将鼠标操作集成到我的程序中。我已尝试通过代码执行此操作: var-boxelem=document.getElementsByClassName(“box”) 然后将鼠标悬停事件侦听器
document.getElementByClassName(“box”)
找不到包含这些框的所有物理属性的名为box的类
我试图分配一个变量boxelem
,以包含每个单独框的位置属性,以便将来可以将鼠标操作集成到我的程序中。我已尝试通过代码执行此操作:var-boxelem=document.getElementsByClassName(“box”)代码>
然后将鼠标悬停事件侦听器添加到boxelem
必要代码:
var canvas;
var ctx;
var box = [];
var boxelem;
//Startup Code
window.onload = function(e) {
canvas = document.getElementById("c");
ctx = canvas.getContext("2d");
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
box = [new box(10, 20, "cyan"), new box(299, 40, "red"), new box(90, 50,
"black"), new box(29, 20, "turquoise")];
boxelem = document.getElementsByClassName("box");
noscroll();
update();
}
//Physic Clock (For real-time physics)
var clock = {
lasttick: 0,
tick: function() {
var td = performance.now() - this.lasttick;
this.lasttick = performance.now();
return td / 1000;
},
reset: function() {
}
}
//Box objects be created here (Box Class)
var box = function(x, y, color) {
var _this = this;
//First Spawn Physics and Settings
_this.x = Math.random() * (canvas.width - 50);
_this.y = Math.random() * (canvas.height - 50);
_this.vx = 0;
_this.vy = Math.random() * 150;
_this.ax = 0;
_this.ay = 440;
_this.color = color;
_this.draw = function() {
ctx.fillStyle = _this.color;
ctx.fillRect(_this.x, _this.y, 50, 50);
}
//Normal Physics
_this.update = function(t, mX, mY) {
if (mX != 0) {
_this.x += _this.vx * t;
_this.vx += mX * t;
} else {
_this.x += _this.vx * t;
_this.vx += _this.ax * t;
}
_this.y += _this.vy * t;
_this.vy += _this.ay * t;
//Boundary Creation
if ((_this.y + 55) > canvas.height) {
_this.vy -= _this.ay * t;
_this.vy = 0;
}
if ((_this.x + 55) > canvas.width) {
_this.vx -= _this.ax * t;
_this.vx = 0;
}
if ((_this.y) < 0) {
_this.vy -= _this.ay * t;
_this.vy = 0;
_this.y = (canvas.height + 20);
}
if ((_this.x) < 0) {
_this.vx -= _this.ax * t;
_this.vx = 0;
}
}
}
//Get mouse position if over a box
var pageX = 0;
var pageY = 0;
for (var z = 0; z < box.length; z++) {
boxelem.addEventListener("mouse", mPos, false);
}
我已经查看了()和(),但不确定如何将其应用于我的问题。您的循环主体没有访问索引。另外,您使用的.length
来自框
函数,而不是框
集合
这:
我没有看到带有类框的元素。因此,方法document.getElementsByClassName(“box”)
总是返回一个空数组。document.getElementByClassName()的可能重复引用JS中实例化的类而不是HTML@D.Simondocument.getElementsByClassName(“box”)
查找具有给定类的HTML元素。因为JS没有真正的类,所以找不到JavaScript类
。我现在明白了,尽管我如何引用box类的元素而不在HTML中创建类?你是对的。但是实际的问题是,boxelem
没有定义。@D.Simon:谢谢,我也添加了一个关于这一点的注释。这意味着将fetch语句移动到window.onload函数之前,对吗?@KyleMyott:如果这样做,并且脚本位于页面顶部,那么它将返回一个空集合。您可以在窗口中移动所有代码。onload
,或者在页面加载时运行的另一个事件
<!DOCTYPE html>
<html lang="en" xmlns="http://www.w3.org/1999/xhtml">
<head>
<script type=text/javascript src="Physics.js"></script>
<meta charset="utf-8" />
<title>Physics Engine of Boxes</title>
</head>
<body>
<canvas id="c"></canvas>
</body>
</html>
for (var z = 0; z < box.length; z++)
{
boxelem.addEventListener("mouse", mPos, false);
}
for (var z = 0; z < boxelem.length; z++)
{
boxelem[z].addEventListener("mouse", mPos, false);
}
//Startup Code
window.onload = function(e) {
var canvas = document.getElementById("c");
var ctx = canvas.getContext("2d");
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
var box = [new box(10, 20, "cyan"), new box(299, 40, "red"), new box(90, 50,
"black"), new box(29, 20, "turquoise")];
var boxelem = document.getElementsByClassName("box");
noscroll();
update();
//Physic Clock (For real-time physics)
var clock = {
lasttick: 0,
tick: function() {
var td = performance.now() - this.lasttick;
this.lasttick = performance.now();
return td / 1000;
},
reset: function() {
}
}
//Box objects be created here (Box Class)
var box = function(x, y, color) {
// ...implementation...
}
//Get mouse position if over a box
var pageX = 0;
var pageY = 0;
for (var z = 0; z < boxelem.length; z++) {
boxelem[z].addEventListener("mouse", mPos, false);
}
}