# Shims

When shims are enabled (which is the default), TS Bridge will automatically use it to provide shims for certain APIs that are not available in the target environment. This is useful for using APIs specific to CommonJS environments such as __dirname and __filename, or import.meta.url in ESM environments.

This means that you can use these APIs in your TypeScript code, and TS Bridge will automatically provide the necessary shims when compiling the code. This makes it easier to write code that works in both CommonJS and ESM environments.

The following shims are available:

• For CommonJS environments:
  • import.meta.url
• For ESM environments:
  • __dirname
  • __filename
  • require (and require.resolve)

The following example demonstrates how TS Bridge compiles code that uses the __dirname global variable:

import { resolve } from 'path';

function getFile(filePath: string) {
  return resolve(__dirname, filePath);
}

When compiled with TS Bridge, the code will work in both CommonJS and ESM environments, as the necessary shims will be provided injected into the output code. The ESM version of the code will look something like this:

function $__dirname(url) {
  // Some logic to get the directory name from `import.meta.url`.
}

import { resolve } from 'path';

function getFile(filePath) {
  return resolve($__dirname(import.meta.url), filePath);
}

The CommonJS version of the code will not include the shims, as they are not needed in CommonJS environments. The output will look something like this:

const path_1 = require('path');

function getFile(filePath) {
  return path_1.resolve(__dirname, filePath);
}