How To Fix Canvas.getContext Is Not A Function Javascript Error

I wrote an Html file that contains some javascript code. It is an Html5 file, so I add a canvas in the Html source code and get the canvas context object with the code move_canvas.getContext(‘2d’);. But when I browse the Html5 file in a web browser, it shows the error message Uncaught TypeError: move_canvas.getContext is not a function in the browser inspector console, this article will tell you how to fix it.

1. How To Debug & Fix The Canvas.getContext Is Not A Function Javascript Error.

  1. Open the Html file in a web browser such as Google Chrome.
  2. Right-click the web page screen in the web browser, then click the Inspect menu item to open the browser inspector.
  3. Click the Sources tab on the inspector, then select the javascript js file or Html file below the Sources tab.
  4. Click the first column in the js code to set a breakpoint at the code that throws the canvas.getContext is not a function error.
  5. Now run the javascript code until it stops at the breakpoint.
  6. Hover the mouse pointer on the canvas object, it will show you the Html object attributes list with the title canvas#move-canvas.
  7. The text before the # charactor is the Html element type, it should be canvas because we just add the canvas object.
  8. The text after the # charactor is the Html element id.
  9. In my example, the Html element debug info is input#move-canvas.
  10. From the above info, we can see the Html object is an input element in my example, it is not a canvas element.
  11. The Html input element has the same id as the canvas element, and the input element does not have the getContext() function.
  12. Then when it runs to the code line canvas.getContext(‘2d’);, it will throw the error Uncaught TypeError: move_canvas.getContext is not a function because the Html input element doese not have the getContext(‘2d’) function.
  13. After I change the input element’s id to a different one from the canvas element’s id, the error has been fixed.
  14. I also find another signal that can be used to find the cause, that is when I assign the width or height value to the canvas object ( canvas.width = canvasWidth; ), the canvas object’s width is always 0 because the Html input element does not support the width attribute.

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