Seems like the jsfiddle is working fine.
You need to create a text file say dataPoints.txt with the content as shown below, browse it using the Choose File input and click Open.

pos 0.20
neg 0.17
neg 0.43
pos 0.13
pos 0.27
neg 0.19
neg 0.49
pos 0.12

If you are still facing any issue kindly reproduce the same in jsfiddle so that we can look into the issue and help you better.

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Suyash Singh
Team CanvasJS