JSChart internally depends on jQuery so you have to refer the jQuery also on the externals section and add a dependency to jQuery in JSChart reference in the external section.
Also, in the code you have to use either import or require on jsChart and once you have done all the pre-requisites you should be able to use the method.
Why don't you try using the npm package available for Chart.js? It would be a straight forward method instead of using all the externals section configuration. Please refer the below link
Installation · Chart.js documentation
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