javascript - Tainted canvas error thrown when refreshing the page with F5 -


i have problem code, quite similar codepen. 

var img = new image();  img.src = 'https://upload.wikimedia.org/wikipedia/commons/thumb/6/63/diceros_bicornis.jpg/320px-diceros_bicornis.jpg';  img.crossorigin = "anonymous"  var canvas = document.getelementbyid('canvas');  var ctx = canvas.getcontext('2d');  img.onload = function() {    ctx.drawimage(img, 0, 0);    img.style.display = 'none';  };  var color = document.getelementbyid('color');  function pick(event) {    var x = event.layerx;    var y = event.layery;    var pixel = ctx.getimagedata(x, y, 1, 1);    var data = pixel.data;    var rgba = 'rgba(' + data[0] + ', ' + data[1] +               ', ' + data[2] + ', ' + (data[3] / 255) + ')';    color.style.background =  rgba;    color.textcontent = rgba;  }  canvas.addeventlistener('mousemove', pick);
<!-- learn code on mdn: https://developer.mozilla.org/en-us/docs/web/api/canvas_api/tutorial/pixel_manipulation_with_canvas -->    <canvas id="canvas" width="300" height="227" style="float:left"></canvas>  <div id="color" style="width:200px;height:50px;float:left"></div>

it somehow works when page first open. when refresh page f5, sometimes starts throwing tainted canvas error. when click x close tab, , click link again open brand new tab work again.

i have img.crossorigin = "anonymous".

that sounds chrome bug, workaround-able : set crossorigin attribute first.

the first time request made, crossorigin attribute set before image has loaded, hence browser redo request.

but when reload page, image cached, , loads before crossorigin attribute set. canvas tainted.

for similar little bugs cases, should define onload event handler before setting src attribute :

var canvas = document.getelementbyid('canvas');  var ctx = canvas.getcontext('2d');    var img = new image();  img.crossorigin = "anonymous"  img.onload = function() {    ctx.drawimage(img, 0, 0);    img.style.display = 'none';  };  // set src last  img.src = 'https://upload.wikimedia.org/wikipedia/commons/thumb/6/63/diceros_bicornis.jpg/320px-diceros_bicornis.jpg';    var color = document.getelementbyid('color');  function pick(event) {    var x = event.layerx;    var y = event.layery;    var pixel = ctx.getimagedata(x, y, 1, 1);    var data = pixel.data;    var rgba = 'rgba(' + data[0] + ', ' + data[1] +               ', ' + data[2] + ', ' + (data[3] / 255) + ')';    color.style.background =  rgba;    color.textcontent = rgba;  }  canvas.addeventlistener('mousemove', pick);
<!-- learn code on mdn: https://developer.mozilla.org/en-us/docs/web/api/canvas_api/tutorial/pixel_manipulation_with_canvas -->    <canvas id="canvas" width="300" height="227" style="float:left"></canvas>  <div id="color" style="width:200px;height:50px;float:left"></div>


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