html - Javascript set src attribute of image not working -


i'm working on code takes weather model image , tests pixel's color. here entire code:

<html>  <head>     <meta title="prww precast (v0.1)">     <meta charset="utf-8">  </head>  <body>      <canvas id="canvas" width="1024px" height="764px">          <img id="map" src=""/>      </canvas>      <script>          //time variables         var currentyear = new date().getfullyear();         var currentmonth = new date().getmonth() + 1;         var currentday = new date().getdate();         var currenthour = new date().gethours();         var currentrun;          //formatting time variables urls         if (currentmonth < 10) {             currentmonth = "0" + currentmonth;         }         if (currentday < 10) {             currentday = "0" + currentday;         }          //finding latest model run               if (currenthour >= 0 && currenthour < 6) {             currentrun = "00";         }         if (currenthour >= 6 && currenthour < 12) {             currentrun = "06";         }         if (currenthour >= 12 && currenthour < 18) {             currentrun = "12";         }         if (currenthour >= 18 && currenthour < 24) {             currentrun = "18";     }     var currentrun = currentrun;      //creating url     var mapaddress = "http://www.tropicaltidbits.com/analysis/models/gfs/" + currentyear + currentmonth + currentday + currentrun + "/gfs_mslp_pcpn_neus_" + 1 + ".png";      //insert image document     document.getelementbyid("map").setattribute("src", mapaddress);      settimeout(2000);      //load image , image data     document.getelementbyid("canvas").getcontext("2d").drawimage(document.getelementbyid("map"), 0, 0);     document.getelementbyid("map").crossorigin = "anonymous";     var pixelcolor = document.getelementbyid("canvas").getcontext("2d").getimagedata(469,451,1,1).data;      //test pixel data color     if (pixelcolor[0] == 255 && pixelcolor[1] == 255 && pixelcolor[2] == 255 && pixelcolor[3] == 255) {         console.log("the code ran 'if' part of pixelcolor if statement.");     } else {         console.log("the code ran 'else' part of pixelcolor if statement.");     }     </script>

for reason, image supposed displayed in canvas isn't showing up. can tell me why, , how can fix it? want solutions involve html or javascript since beginner.

you need wait image load before can access it.

// use 1 of following 2 lines. var image = new image(); // or  var image = document.getelementbyid("map");  // set image location. image.src = mapaddress; // setting source not mean image has loaded. image.onload = function(event){ // fires when image has loaded. points image     var c = document.createelement("canvas");  // create canvas     c.width = this.width;   // set size match image     c.height = this.height;     this.ctx = c.getcontext("2d");  // 2d context     this.ctx.drawimage(this, 0, 0);  // draw image onto canvas     try{         var imagedat = this.ctx.getimagedata(0,0,this.width,this.height);  // image pixel data         // can access pixel data.       }catch(e){         // if runs can not access image data.         alert("cross origin resticted access");     } } image.onerror = function(event){     // there error loading image.     alert("image '"+this.src+"'\nfailed load!"); }

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