dataPoints is an array of objects. But as per the code shared above, it seems like you are passing a string
("{x: new Date(2017, 10, 20),y: 10},{x: new Date(2017, 10, 17),y: 15}") to dataPoints array instead of objects. Therefore, parsing the data and converting it to objects like {x: new Date(2017, 10, 20),y: 10},{x: new Date(2017, 10, 17),y: 15} should work fine in your case. Here is an example you can refer.
If this doesn’t suit your requirements, Can you please create a JSFiddle, along with your sample data, reproducing the issue?
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Suyash Singh
Team CanvasJS