Add Tell Node To Treat JS Files As ESM as a JavaScript TIL

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://crafty-builder-6996.ck.page/e169c61186).
 
-_1312 TILs and counting..._
+_1313 TILs and counting..._
 
 ---
 
@@ -470,6 +470,7 @@ _1312 TILs and counting..._
 - [String Interpolation With Template Literals](javascript/string-interpolation-with-template-literals.md)
 - [Support Nested Matching In Custom Jest Matchers](javascript/support-nested-matching-in-custom-jest-matchers.md)
 - [Tell Jest To Focus On Running Only One Test](javascript/tell-jest-to-focus-on-running-only-one-test.md)
+- [Tell Node To Treat JS Files As ESM](javascript/tell-node-to-treat-js-files-as-esm.md)
 - [Tell Prettier To Not Format A Statement](javascript/tell-prettier-to-not-format-a-statement.md)
 - [Test Coverage Stats With Jest](javascript/test-coverage-stats-with-jest.md)
 - [Test Timing-Based Code With Jest Fake Timers](javascript/test-timing-based-code-with-jest-fake-timers.md)

javascript/tell-node-to-treat-js-files-as-esm.md

@@ -0,0 +1,24 @@
+# Tell Node To Treat JS Files As ESM
+
+By default, Node will treat all `.js` files as CommonJS. That means you'll need
+to use the CommonJS export and require syntax to share code between files. If
+you'd instead like to opt-in to ESM (ECMAScript Modules), you'll need to update
+your `package.json`.
+
+Add the following line:
+
+```json
+"type": "module",
+```
+
+This will tell node that instead of CJS, it should treat all `.js` files as
+ESM. This means that ESM-based `export` and `import` syntax will work.
+
+This also means you don't need to be defining your files with the `.mjs`
+extension.
+
+For more extensive reading on this, see:
+
+- [ECMAScript Modules in Node.js](https://www.typescriptlang.org/docs/handbook/esm-node.html)
+- [Getting Started with (and Surviving) Node.js ESM](https://formidable.com/blog/2021/node-esm-and-exports/)
+- [`.mts` is a cool file extension (TypeScript ES modules)](https://mtsknn.fi/blog/mts-file-extension/)