CA's rule, which is well described in the previous answers, has been challenged in court. The plaintiff lost. See this web reference for the details:
https://www.coblentzlaw.com/california-office-of-tax-appeals-gives-precedential-authority-to-bindley...
Since you're a resident of NJ, ALL your income is taxable by NJ, regardless of its source. But you may take a credit on your NJ return for any taxes paid to CA, so you won't be double-taxed. (The credit can't exceed what the NJ tax would have been on that income.)
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
