Total typescript essentials - free TS book - Great way to start your journey with Typescript. I have read several chapters and I can certainly say that after reading you will not only understand how to use typescript, but also how it works.
JavaScript
Creating Cancelable Promises in JavaScript - Intresting way to cancel Promises, but only for idempotent api calls and I would recommend to consider using observables for these use cases.
TypeScript
Total typescript essentials - free TS book - Great way to start your journey with Typescript. I have read several chapters and I can certainly say that after reading you will not only understand how to use typescript, but also how it works.
Next.js security list - Great list of things you need to focus when creating Next.js/React app. I would add to VS Code paragraph libraries like checkmarx.