Uncaught TypeError:Cannot read property ‘getContext’ of null

Sruthi S

7y20.3kLearn iOS Programming

Im getting this error:

Uncaught TypeError: Cannot read property 'getContext' of null

in my demo.js page

I have included demo.js page in my html page (start page) .

How can i solve this error?

4 Replies

Know the answer? Post it — somebody with the same question will find it here.

Laxmidhar Sahoo7y ago

I thinkmanoj is currect


$(function() {   
var Grid = function() {   
var canvas = document.getElementById("canvas");  
        if(canvas.getContext) {  
            var context = canvas.getContext("2d");  
    }  
 }   
});

Manoj Bhoir7y ago
I guess the problem is your js runs before the html is loaded.

If you are using jquery, you can use the document ready function to wrap your code:
$(function() {
// codes...
});
Or simply put your js after the
+1
Bryian Tan7y ago
Tough to tell without any code.
0
Afzaal Ahmad Zeeshan7y ago
But you have not shared any of the code samples that you have used to develop the application.
My guess is that you are trying to use the HTML5 canvas element to render something on top of it, in that case the variable that is holding the reference of your canvas is null. Make sure that the canvas element (or whatever element that has this getContext() function) exists in the DOM.
var canvas = document.getElementById("canvas");

if(canvas != null) {
    // do here.
    canvas.getContext("2d");
} else {
    // report the error.
}
This way you can resolve this problem. Do share the code if that doesn't fix the problem.
0