Support for typescript (#3)

* Support for typescript

* Self review

* Fix lint-staged

* Fix  formatting

Author: Joel Denning

README.md

@@ -1,6 +1,8 @@
 # node-loader-extensionless
 
-A node loader that auto-appends .js extensions to imports
+A node loader that auto-appends .js or .ts extensions to imports, based on the parentURL.
+
+When paired with [@node-loader/babel](https://github.com/node-loader/node-loader-babel) loader allows for loading typescript via NodeJS loaders
 
 ## Installation
 

babel.config.json

@@ -0,0 +1,3 @@
+{
+  "presets": ["@babel/preset-typescript"]
+}

lib/node-loader-extensionless.js

@@ -1,13 +1,50 @@
+import { extname, basename } from "node:path";
+
+const typescriptFileExts = [
+  ".ts",
+  ".tsx",
+  ".mts",
+  ".cts",
+  ".d.ts",
+  ".d.mts",
+  ".d.cts",
+  ".js",
+];
+
 export async function resolve(specifier, context, nextResolve) {
-  const pathParts = specifier.split("/");
-  const fileName = pathParts[pathParts.length - 1];
+  const fileName = basename(specifier);
   const isRelativePath =
     specifier.startsWith("./") ?? specifier.startsWith("../");
 
-  // Only add .ts extension to path-like specifiers, not bare specifiers
+  let result;
+
+  // Only add extensions to path-like specifiers, not bare specifiers
   if (isRelativePath && !fileName.includes(".")) {
-    return nextResolve(specifier + ".js", context);
+    const parentFileExt = context.parentURL
+      ? extname(context.parentURL) || ".js"
+      : ".js";
+
+    const isTypescript = typescriptFileExts.includes(parentFileExt);
+    // Mimic the typescript file extension substitution algorithm
+    // Ideally we'd take into account the moduleResolution option, but for now we skip that
+    // https://www.typescriptlang.org/docs/handbook/modules/reference.html#file-extension-substitution
+    const fileExtensionsToTry = isTypescript ? typescriptFileExts : [".js"];
+
+    for (const ext of fileExtensionsToTry) {
+      try {
+        result = await nextResolve(specifier + ext, context);
+        break;
+      } catch {}
+    }
+  } else {
+    result = nextResolve(specifier, context);
+  }
+
+  if (!result) {
+    throw Error(
+      `Could not resolve specifier '${specifier}' from parent URL ${context.parentURL}`,
+    );
   }
 
-  return nextResolve(specifier, context);
+  return result;
 }

package.json

@@ -10,7 +10,7 @@
     "lib"
   ],
   "scripts": {
-    "test": "cross-env node --loader ./lib/node-loader-extensionless.js ./test/run-tests.js",
+    "test": "cross-env node --import=./test/register.js ./test/run-tests.js",
     "lint": "eslint .",
     "check-format": "prettier --check .",
     "prepare": "husky install"
@@ -41,7 +41,10 @@
     "access": "public"
   },
   "devDependencies": {
+    "@babel/core": "^7.23.7",
+    "@babel/preset-typescript": "^7.23.3",
     "@baseplate-sdk/utils": "^3.2.1",
+    "@node-loader/babel": "^2.1.0",
     "cross-env": "^7.0.3",
     "eslint": "^8.56.0",
     "eslint-config-node-important-stuff": "^2.0.0",
@@ -54,6 +57,6 @@
   },
   "lint-staged": {
     "*.js": "eslint --cache --fix",
-    "*.{js,css,md,yml,eslintrc}": "prettier --write"
+    "*.{js,css,md,yml,eslintrc,ts,tsx,json}": "prettier --write"
   }
 }