Problem
It seems to be the case that the canvas animation affects other JavaScript functions when I use window.onload = function() {. Please let me know the best practice to use animation without affecting other JavaScript.
window.onload = function() {
//canvas init
var canvas = document.getElementById("snow");
var ctx = canvas.getContext("2d");
//canvas dimensions
var W = window.innerWidth;
var H = window.innerHeight;
canvas.width = W;
canvas.height = H;
//snowflake particles
var mp = 250; //max particles
var particles = [];
for (var i = 0; i < mp; i++) {
particles.push({
x: Math.random() * W, //x-coordinate
y: Math.random() * H, //y-coordinate
r: Math.random() * 4 + 1, //radius
d: Math.random() * mp //density
});
}
//Lets draw the flakes
function draw() {
ctx.clearRect(0, 0, W, H);
ctx.fillStyle = "rgba(255, 255, 255, 0.8)";
ctx.beginPath();
for (var i = 0; i < mp; i++) {
var p = particles[i];
ctx.moveTo(p.x, p.y);
ctx.arc(p.x, p.y, p.r, 0, Math.PI * 2, true);
}
ctx.fill();
update();
}
//Function to move the snowflakes
//angle will be an ongoing incremental flag. Sin and Cos functions will be applied to it to create vertical and horizontal movements of the flakes
var angle = 0;
function update() {
angle += 0.01;
for (var i = 0; i < mp; i++) {
var p = particles[i];
//Updating X and Y coordinates
//We will add 1 to the cos function to prevent negative values which will lead flakes to move upwards
//Every particle has its own density which can be used to make the downward movement different for each flake
//Lets make it more random by adding in the radius
p.y += Math.cos(angle + p.d) + 1 + p.r / 2;
p.x += Math.sin(angle) * 2;
//Sending flakes back from the top when it exits
//Lets make it a bit more organic and let flakes enter from the left and right also.
if (p.x > W + 5 || p.x < -5 || p.y > H) {
if (i % 3 > 0) {
//66.67% of the flakes
particles[i] = {
x: Math.random() * W,
y: -10,
r: p.r,
d: p.d
};
} else {
//If the flake is exitting from the right
if (Math.sin(angle) > 0) {
//Enter from the left
particles[i] = {
x: -5,
y: Math.random() * H,
r: p.r,
d: p.d
};
} else {
//Enter from the right
particles[i] = {
x: W + 5,
y: Math.random() * H,
r: p.r,
d: p.d
};
}
}
}
}
}
//animation loop
setInterval(draw, 33);
};body {
background: tomato;
}<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<canvas id="snow" style="display:block;position:fixed;z-index:999;pointer-events:none;"></canvas>Solution
One solution to allow multiple functions called when the page loads is to add a callback using EventTarget.addEventListener() for the DOMContentLoaded event.
window.addEventListener('DOMContentLoaded', function() {
//canvas init
//..
});
One could also simply use the load event. Many believe that modern browsers typically won’t have DOM elements not query-able via JavaScript- especially if the script tag is loaded in the <body> tag instead of the <head> tag, and thus one wouldn’t need to wait for the DOMContentLoaded event.