unit test raises error because of .getContext() is not implemented

javascript canvas jestjs jsdom
lpie88 picture lpie88 · Feb 16, 2018 · Viewed 13.9k times · Source

I am writing tests using Jest for components that use canvas elements. I keep getting an error when I run my tests that looks like this.

Error: Not implemented: HTMLCanvasElement.prototype.getContext (without installing the canvas npm package)

From my understanding Jest uses jsdom for its testing and that jsdom is compatible with canvas if you install the canvas or canvas-prebuilt packages.

I have tried installing each of these packages and neither of them have resolved the error. The only thing that I think could be going wrong is that jsdom cannot find the canvas or canvas-prebuilt packages. Does anyone know a way to fix this error or test to see if jsdom is finding the other packages? Thanks a lot!

Answer

Red Mercury picture Red Mercury · Feb 17, 2018

You can create your own mock of the function in a jest setup script 

HTMLCanvasElement.prototype.getContext = () => { 
  // return whatever getContext has to return
};

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