Migrating a Next.js project from JavaScript to TypeScript enhances code quality, debugging, and developer experience by improving auto-completion, linting, and readability. TypeScript is a superset of JavaScript that adds static typing, making the code more reliable with earlier detection of bugs and minimization of runtime errors. The language provides explicit type annotations, aliases, and interfaces to define object structure and properties, reducing ambiguity and making code easier to understand. To integrate TypeScript into an existing Next.js project, developers must install the necessary packages, create a tsconfig.json file, rename JavaScript files to TypeScript equivalents, and use tools like DefinitelyTyped for type definitions of external libraries. With TypeScript, developers can take advantage of features like interface contracts, compile-time errors, and seamless integration with Contentful's REST API and GraphQL API to build faster, more reliable, and user-friendly digital experiences.