Module mode vs script mode in Typescript

Typescript parses each of our Typescript files into one of two modes:

• module mode: the file has any imports or exports
• script mode: the file does not use any imports or exports

We’ll almost always want to stick to Module mode.

Script mode

In script mode, any top-level variables we declare will be available to other files in the project without an explicit import, and we can safely consume global exports from third-party UMD modules without explicitly importing them first.

Use cases of script mode:

1. To quickly prototype browser code that you plan to compile to no module system at all ({"module": "none"}) in tsconfig.json and include as raw <script /> tags in HTML file.
2. to create type declarations