Yes, it is possible to generate TypeScript declaration files from a JavaScript library. There are several methods and tools available to achieve this, catering to different scenarios and requirements. Here's an overview of the approaches:
Manual Declaration Files: One basic approach is to manually create declaration files for existing JavaScript libraries. This method involves writing .d.ts files that describe the types, functions, and objects provided by the JavaScript library. Manual creation is particularly useful when the library does not provide its own declaration file. For example, to create a declaration file for a library named lodash, you would start with a file named lodash.d.ts and declare the modules and their exports within[1].
Using TypeScript Compiler (tsc) Options: The TypeScript compiler itself can be configured to generate declaration files for JavaScript code. By setting the allowJs, declaration, and outDir options in the tsconfig.json file, you can instruct the TypeScript compiler to process JavaScript files and generate corresponding .d.ts files in a specified output directory. This method is suitable for generating declaration files for your own JavaScript code[1].
Automated Tools: There are tools designed specifically to automate the generation of TypeScript declaration files from JavaScript code. For example, dts-gen is a tool recommended by Microsoft as a starting point for creating declaration files. It attempts to generate a basic .d.ts file for a given JavaScript module, which can then be manually refined and extended. Another tool, dtsmake, utilizes Ternjs for generating declaration files and is noted for its promise in handling complex type inference[2].
Community Tools and Libraries: The TypeScript community has developed various tools and libraries to assist in converting JavaScript codebases to TypeScript, including generating declaration files. For instance, jsdoc-to-typescript-declaration is a tool that converts Closure-style JSDoc type annotations to TypeScript definition files, aiming to assist developers in writing TypeScript definitions for large libraries[16].
Research and Development Tools: There are ongoing research and development efforts to improve ...
