Javascript error in rails

Question

i start to learn javascript with easy game tutorial http://www.youtube.com/watch?v=U7anheKJSaIand on RoR got error in index.html.erb:

<script>
 var ctx, canvas;
 var data;
 window.onload = function main(){
 canvas = document.createElement("canvas");
 canvas.width = canvas.height = 200;
 ctx = canvas.getContext("2d");
 document.body.appendChild(canvas);
 init();
 tick();
 } 
 function init(){
 data = new Tile(20,20);
 }
 function tick(){
 window.requestAnimationFrame(tick);
 update();
 render();
 }
 function update(){}
 function render(){
 data.draw(ctx);
 }
 function Tile(x,y){
 var x = x, y = y;
 var tile = Tile.BlANK;
 if(tile == null){
 var _c = document.createElement("canvas");
 _c.width = _c.height = 100;
 _ctx = _c.getContext("2d");
 _ctx.fillStyle = "skyblue";
 //blank
 _ctx.fillRect(0,0,100,100);
 Tile.BlANK = new Image();
 Tile.BLANK.src = _c.toDataURL();
 tile = Tile.BLANK;
 } 
 this.update = function(){} 
 this.draw = function(ctx){
 ctx.drawImage(tile, x, y);
 }
}
</script>

and this is error:

Tile.BLANK.src = _c.toDataURL();

Uncaught TypeError: Cannot set property src of undefined

Answer 1

Your error is here

Tile.BlANK = new Image();

It should be:

Tile.BLANK = new Image();

The error comes from .BlANK and it's because there is a typo. The l (L) is lowecase, and therefore later when you are trying to access the .src in you can't, because the real .BLANK is still undefined.

This is in function Tile(x,y){...}, but you also have the typo some other places. Just check your code for lowercase letters in .BLANK.

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