From 53e470d3fcede36056799f44f9f6885a9e479b33 Mon Sep 17 00:00:00 2001
From: Blake Embrey <hello@blakeembrey.com>
Date: Fri, 14 Jun 2019 17:45:48 -0700
Subject: [PATCH] Simplify extension ordering for preferences

---
 README.md              |  2 +-
 src/bin.ts             | 14 +++++++-------
 src/index.spec.ts      |  6 ++++++
 src/index.ts           | 22 +++++++++-------------
 tests/require-cache.ts |  7 +++++++
 tsconfig.json          |  2 +-
 6 files changed, 31 insertions(+), 22 deletions(-)
 create mode 100644 tests/require-cache.ts

diff --git a/README.md b/README.md
index 5c1cd44b3..bed60d1c6 100644
--- a/README.md
+++ b/README.md
@@ -136,7 +136,7 @@ _Environment variable denoted in parentheses._
 * `--skip-project` Skip project config resolution and loading (`TS_NODE_SKIP_PROJECT`, default: `false`)
 * `--skip-ignore` Skip ignore checks (`TS_NODE_SKIP_IGNORE`, default: `false`)
 * `--log-error` Logs errors of types instead of exit the process (`TS_NODE_LOG_ERROR`, default: `false`)
-* `--prefer-ts-exts` Changes the order of file extensions used when matching file imports so that `.ts` files are preferred over `.js` (`TS_PREFER_TS_EXTS`, default: `false`)
+* `--prefer-ts-exts` Re-order file extensions so that TypeScript imports are preferred (`TS_NODE_PREFER_TS_EXTS`, default: `false`)
 
 ### Programmatic Only Options
 
diff --git a/src/bin.ts b/src/bin.ts
index 1c5241e07..dd6e01586 100644
--- a/src/bin.ts
+++ b/src/bin.ts
@@ -109,6 +109,13 @@ const cwd = process.cwd()
 const code = args['--eval']
 const isPrinted = args['--print'] !== undefined
 
+/**
+ * Eval helpers.
+ */
+const EVAL_FILENAME = `[eval].ts`
+const EVAL_PATH = join(cwd, EVAL_FILENAME)
+const EVAL_INSTANCE = { input: '', output: '', version: 0, lines: 0 }
+
 // Register the TypeScript compiler instance.
 const service = register({
   files,
@@ -139,13 +146,6 @@ if (version >= 2) {
 // Require specified modules before start-up.
 if (args['--require']) (Module as any)._preloadModules(args['--require'])
 
-/**
- * Eval helpers.
- */
-const EVAL_FILENAME = `[eval].ts`
-const EVAL_PATH = join(cwd, EVAL_FILENAME)
-const EVAL_INSTANCE = { input: '', output: '', version: 0, lines: 0 }
-
 // Prepend `ts-node` arguments to CLI for child processes.
 process.execArgv.unshift(__filename, ...process.argv.slice(2, process.argv.length - args._.length))
 process.argv = [process.argv[1]].concat(args._.length ? resolve(cwd, args._[0]) : []).concat(args._.slice(1))
diff --git a/src/index.spec.ts b/src/index.spec.ts
index c9bf83ee4..e0905cadc 100644
--- a/src/index.spec.ts
+++ b/src/index.spec.ts
@@ -326,6 +326,12 @@ describe('ts-node', function () {
       expect(m.example()).to.equal('hello')
     })
 
+    it('should work with `require.cache`', function () {
+      const { example1, example2 } = require('../tests/require-cache')
+
+      expect(example1).to.not.equal(example2)
+    })
+
     it('should use source maps', function (done) {
       try {
         require('../tests/throw')
diff --git a/src/index.ts b/src/index.ts
index ef786cca8..82aadb328 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -420,7 +420,7 @@ function shouldIgnore (filename: string, ignore: RegExp[]) {
  *
  * @param {string} ext
  */
-function refreshRequireExtension (ext: string) {
+function reorderRequireExtension (ext: string) {
   const old = require.extensions[ext] // tslint:disable-line
   delete require.extensions[ext] // tslint:disable-line
   require.extensions[ext] = old // tslint:disable-line
@@ -436,21 +436,17 @@ function registerExtensions (
   register: Register,
   originalJsHandler: (m: NodeModule, filename: string) => any
 ) {
-  if (opts.preferTsExts) {
-    extensions.unshift(
-      '.ts',
-      '.tsx',
-      ...Object.keys(require.extensions), // tslint:disable-line
-    )
+  // Register new extensions.
+  for (const ext of extensions) {
+    registerExtension(ext, ignore, register, originalJsHandler)
   }
 
-  // @todo a better way with options
-  Array.from(new Set(extensions))
-       .forEach(ext => {
-         registerExtension(ext, ignore, register, originalJsHandler)
+  if (opts.preferTsExts) {
+    // tslint:disable-next-line
+    const preferredExtensions = new Set([...extensions, ...Object.keys(require.extensions)])
 
-         if (ext in require.extensions) refreshRequireExtension(ext) // tslint:disable-line
-       })
+    for (const ext of preferredExtensions) reorderRequireExtension(ext)
+  }
 }
 
 /**
diff --git a/tests/require-cache.ts b/tests/require-cache.ts
new file mode 100644
index 000000000..4fbdd5047
--- /dev/null
+++ b/tests/require-cache.ts
@@ -0,0 +1,7 @@
+const moduleName = require.resolve('./module')
+
+const { example: example1 } = require(moduleName)
+delete require.cache[moduleName]
+const { example: example2 } = require(moduleName)
+
+export { example1, example2 }
diff --git a/tsconfig.json b/tsconfig.json
index 447b83c08..486a70bae 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -1,6 +1,6 @@
 {
   "compilerOptions": {
-    "target": "es5",
+    "target": "es2015",
     "lib": ["es2015"],
     "rootDir": "src",
     "outDir": "dist",