The reason why software must have a license is because two actions are otherwise not allowed by copyright law:
- Distributing software (giving others exact copies)
- Distributing modified versions
The license of CanvasJS permits distribution under certain conditions. For the developer license,
You are allowed to distribute CanvasJS Software along with your Applications to the end-users.
As phrased, and I am not a lawyer, the developer license of CanvasJS does not allow distribution of CanvasJS to other developers. If you wish to include CanvasJS source code in, say, a Github repo with your own library, I suggest contacting Fenopix to clarify whether this is allowed by the license. I suspect they would say no.
The website license does not permit distribution in the sense of someone obtaining CanvasJS source from a Github repo in which you also have your application either.
You can release your library under any license terms you wish, including MIT, provided:
- Your library is not a derivative work of CanvasJS. (If it is, you are in the same situation as if you were trying to distribute CanvasJS with modifications.)
- You only release the source code of your library and not any source code of CanvasJS. (Users would need to obtain their own copy of CanvasJS on their own.)
The subject of what software is or is not a derivative work of other software is a complex question - see for example here. To be sure, you may inquire with CanvasJS whether they consider your library a derivative work, or inquire with a copyright lawyer.