我有2个脚本（JS + CANVAS），每个页面都不需要，但它们包含在一个全局JS文件中，因此出现了几个控制台错误。
我设法通过在运行脚本之前检查父div在页面上解决了类似的问题，方法是将它包装起来：if ($('#parent-div').length > 0) {} ...但是我似乎无法将其转换为使用我遇到问题的其他脚本。
脚本的第一位相对较短：
$(function(){
var scene = document.getElementById('metropallax');
var parallaxInstance = new Parallax(scene, {
relativeInput: true,
calibrateX: false,
calibrateY: true,
invertX: false,
invertY: true,
limitX: false,
//limitY: 10,
limitY: 0,
scalarX: 2,
scalarY: 8,
frictionX: 0.2,
frictionY: 0.8,
originX: 0.0,
originY: 1.0
});
});
我会认为我之前给出的例子对此很有效，但显然不是。可能是在做一些愚蠢/遗漏的事情。
canvas脚本非常漫长，但我会将其全部包含在内，因为我认为这是最好的：
$(function(){
// Create an array to store our particles
var particles = [];
// The amount of particles to render
var particleCount = 8;
// Orig 30
// The maximum velocity in each direction
var maxVelocity = 4;
// The target frames per second (how often do we want to update / redraw the scene)
var targetFPS = 24;
// Orig 33
// Set the dimensions of the canvas as variables so they can be used.
var canvasWidth = 400;
var canvasHeight = 400;
// Create an image object (only need one instance)
var imageObj = new Image();
// Once the image has been downloaded then set the image on all of the particles
imageObj.onload = function() {
particles.forEach(function(particle) {
particle.setImage(imageObj);
});
};
// Once the callback is arranged then set the source of the image
imageObj.src = "http://www.blog.jonnycornwell.com/wp-content/uploads/2012/07/Smoke10.png";
// A function to create a particle object.
function Particle(context) {
// Set the initial x and y positions
this.x = 0;
this.y = 0;
// Set the initial velocity
this.xVelocity = 0;
this.yVelocity = 0;
// Set the radius
this.radius = 5;
// Store the context which will be used to draw the particle
this.context = context;
// The function to draw the particle on the canvas.
this.draw = function() {
// If an image is set draw it
if(this.image){
this.context.drawImage(this.image, this.x-128, this.y-128);
// If the image is being rendered do not draw the circle so break out of the draw function
return;
}
// Draw the circle as before, with the addition of using the position and the radius from this object.
this.context.beginPath();
this.context.arc(this.x, this.y, this.radius, 0, 2 * Math.PI, false);
this.context.fillStyle = "rgba(0, 255, 255, 1)";
this.context.fill();
this.context.closePath();
};
// Update the particle.
this.update = function() {
// Update the position of the particle with the addition of the velocity.
this.x += this.xVelocity;
this.y += this.yVelocity;
// Check if has crossed the right edge
if (this.x >= canvasWidth) {
this.xVelocity = -this.xVelocity;
this.x = canvasWidth;
}
// Check if has crossed the left edge
else if (this.x <= 0) {
this.xVelocity = -this.xVelocity;
this.x = 0;
}
// Check if has crossed the bottom edge
if (this.y >= canvasHeight) {
this.yVelocity = -this.yVelocity;
this.y = canvasHeight;
}
// Check if has crossed the top edge
else if (this.y <= 0) {
this.yVelocity = -this.yVelocity;
this.y = 0;
}
};
// A function to set the position of the particle.
this.setPosition = function(x, y) {
this.x = x;
this.y = y;
};
// Function to set the velocity.
this.setVelocity = function(x, y) {
this.xVelocity = x;
this.yVelocity = y;
};
this.setImage = function(image){
this.image = image;
}
}
// A function to generate a random number between 2 values
function generateRandom(min, max){
return Math.random() * (max - min) + min;
}
// The canvas context if it is defined.
var context;
// Initialise the scene and set the context if possible
function init() {
var canvas = document.getElementById('smoke');
if (canvas.getContext) {
// Set the context variable so it can be re-used
context = canvas.getContext('2d');
// Create the particles and set their initial positions and velocities
for(var i=0; i < particleCount; ++i){
var particle = new Particle(context);
// Set the position to be inside the canvas bounds
particle.setPosition(generateRandom(0, canvasWidth), generateRandom(0, canvasHeight));
// Set the initial velocity to be either random and either negative or positive
particle.setVelocity(generateRandom(-maxVelocity, maxVelocity), generateRandom(-maxVelocity, maxVelocity));
particles.push(particle);
}
}
else {
alert("Please use a modern browser");
}
}
// The function to draw the scene
function draw() {
// Clear the drawing surface and fill it with a black background
context.fillStyle = "rgba(0, 0, 0, 0.5)";
context.fillRect(0, 0, 400, 400);
// Go through all of the particles and draw them.
particles.forEach(function(particle) {
particle.draw();
});
}
// Update the scene
function update() {
particles.forEach(function(particle) {
particle.update();
});
}
// Initialize the scene
init();
// If the context is set then we can draw the scene (if not then the browser does not support canvas)
if (context) {
setInterval(function() {
// Update the scene befoe drawing
update();
// Draw the scene
draw();
}, 1000 / targetFPS);
}
});
我假设那里有一些我可以使用if声明定位的内容，但我还没有找到它。有人可以建议吗？
答案 0 :(得分：1)
我不知道这是否适合您，但我会使用放在body元素上的类来指示脚本是否应该运行。类似的东西：
--advertise-host检查每个脚本开头的课程。
或者您可以尝试使用RequireJS之类的东西来加载所需的js文件，这些文件基于上面提到的类机制，并且如果不需要则跳过加载文件。