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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>

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  • \$\begingroup\$ Can you explain what you mean by "It seems to be the canvas animation effects to other javaScript functions"? do other javascript functions not work the same after adding that onload callback? \$\endgroup\$ – Sᴀᴍ Onᴇᴌᴀ Nov 27 '17 at 17:33
  • \$\begingroup\$ @SamOnela I mean it override every other attached onload function \$\endgroup\$ – Muhammed Nov 27 '17 at 17:34
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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.

window.addEventListener('DOMContentLoaded', 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);
});
window.addEventListener('DOMContentLoaded', function() {
  console.log('another onload callback');
});
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>

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