Dual emitting using tshy

The Azure SDK for JS client libraries are built for both CommonJS and ESM.

While the two formats are largely compatible, a few caveats apply.

Usage of __dirname and __filename

When a module is required in commonJS, __dirname and __filename are available via the module system; however, in ESM the same globals* are not available.

Likewise, in CommonJS the globals import.meta.* are not available for usage.

Our build tool, isaacs/tshy provides a mechanism for automatically polyfilling the correct syntax depending on the import type.

In order to properly fetch the current filename or current dirname you could do the following:

// myFile.ts - ESM flavor, use import.meta
const currentDir = dirname(fileURLToPath(import.meta.url));

// myFile-cjs.cts - CommonJS flavor, use __dirname and __filename
const currentDir = __dirname

Note that the file naming convention is important! The commonJS polyfill must:

1. begin with the same file name as the ESM flavor
2. Add the -cjs postfix to the file name
3. Use .cts extension