TS1235: A namespace declaration is only allowed at the top level of a namespace or module

TypeScript is a powerful programming language that builds on JavaScript by adding static types, allowing developers to define the type of data each variable can hold and catch errors during development. This feature ensures safer and more reliable code. TypeScript is a superset language, meaning it takes all the functionalities of JavaScript and expands upon it by adding more features, such as static typing, interfaces, and enums. Any valid JavaScript code is also valid TypeScript code, allowing developers to gradually adopt TypeScript in existing JavaScript projects. A namespace in TypeScript is used to group logically related code into a single unit, avoiding global scope pollution. However, a namespace can only be declared at the top level of a module or another namespace. The TS1235 error occurs when a namespace is declared in a place where it's not allowed, such as inside another namespace or function. To fix this error, the namespace must be declared at the top level. Namespaces help in organizing code and avoiding naming collisions, but they must be declared correctly. It's also possible to nest namespaces inside one another, but the outer namespace must be at the top level. By understanding the constraints and structures of TypeScript, developers can navigate the language effectively and avoid unnecessary errors.