README.md

@@ -114,6 +114,8 @@ You can set options by passing them before the script path, via programmatic usa
 ts-node --compiler ntypescript --project src/tsconfig.json hello-world.ts
 ```
 
+**Note:** [`ntypescript`](https://github.com/TypeStrong/ntypescript#readme) is an example of a TypeScript compatible `compiler`.
+
 ### CLI Options
 
 Supports `--print`, `--eval` and `--require` from [node.js CLI options](https://nodejs.org/api/cli.html).
@@ -140,7 +142,7 @@ _Environment variable denoted in parentheses._
 
 ### Programmatic Only Options
 
-* `transformers` An array of transformers to pass to TypeScript
+* `transformers` `_ts.CustomTransformers | ((p: _ts.Program) => _ts.CustomTransformers)` An object with transformers or a function that accepts a program and returns an transformers object to pass to TypeScript. Function isn't available with `transpileOnly` flag
 * `readFile` Custom TypeScript-compatible file reading function
 * `fileExists` Custom TypeScript-compatible file existence function
 

package.json

@@ -1,6 +1,6 @@
 {
   "name": "ts-node",
-  "version": "8.3.0",
+  "version": "8.4.0",
   "description": "TypeScript execution environment and REPL for node.js, with source map support",
   "main": "dist/index.js",
   "types": "dist/index.d.ts",

src/index.spec.ts

@@ -288,6 +288,15 @@ describe('ts-node', function () {
       })
     })
 
+    it('should import ts before js when TS_NODE_PREFER_TS_EXTS env is present', function (done) {
+      exec(`${BIN_EXEC} tests/import-order/compiled`, { env: { ...process.env, TS_NODE_PREFER_TS_EXTS: 'true' } }, function (err, stdout) {
+        expect(err).to.equal(null)
+        expect(stdout).to.equal('Hello, TypeScript!\n')
+
+        return done()
+      })
+    })
+
     it('should ignore .d.ts files', function (done) {
       exec(`${BIN_EXEC} tests/import-order/importer`, function (err, stdout) {
         expect(err).to.equal(null)

src/index.ts

@@ -71,7 +71,7 @@ export interface Options {
   ignoreDiagnostics?: Array<number | string>
   readFile?: (path: string) => string | undefined
   fileExists?: (path: string) => boolean
-  transformers?: _ts.CustomTransformers
+  transformers?: _ts.CustomTransformers | ((p: _ts.Program) => _ts.CustomTransformers)
 }
 
 /**
@@ -274,32 +274,23 @@ export function register (opts: Options = {}): Register {
   /**
    * Create the basic required function using transpile mode.
    */
-  let getOutput = function (code: string, fileName: string, lineOffset = 0): SourceOutput {
-    const result = ts.transpileModule(code, {
-      fileName,
-      transformers,
-      compilerOptions: config.options,
-      reportDiagnostics: true
-    })
-
-    const diagnosticList = result.diagnostics ?
-      filterDiagnostics(result.diagnostics, ignoreDiagnostics) :
-      []
-
-    if (diagnosticList.length) reportTSError(configDiagnosticList)
-
-    return [result.outputText, result.sourceMapText as string]
-  }
-
-  let getTypeInfo = function (_code: string, _fileName: string, _position: number): TypeInfo {
-    throw new TypeError(`Type information is unavailable without "--type-check"`)
-  }
+  let getOutput: (code: string, fileName: string, lineOffset: number) => SourceOutput
+  let getTypeInfo: (_code: string, _fileName: string, _position: number) => TypeInfo
 
   // Use full language services when the fast option is disabled.
   if (typeCheck) {
     const memoryCache = new MemoryCache(config.fileNames)
     const cachedReadFile = cachedLookup(debugFn('readFile', readFile))
 
+    const getCustomTransformers = () => {
+      if (typeof transformers === 'function') {
+        const program = service.getProgram()
+        return program ? transformers(program) : undefined
+      }
+
+      return transformers
+    }
+
     // Create the compiler host for type checking.
     const serviceHost: _ts.LanguageServiceHost = {
       getScriptFileNames: () => Array.from(memoryCache.fileVersions.keys()),
@@ -331,14 +322,14 @@ export function register (opts: Options = {}): Register {
       getCurrentDirectory: () => cwd,
       getCompilationSettings: () => config.options,
       getDefaultLibFileName: () => ts.getDefaultLibFilePath(config.options),
-      getCustomTransformers: () => transformers
+      getCustomTransformers: getCustomTransformers
     }
 
     const registry = ts.createDocumentRegistry(ts.sys.useCaseSensitiveFileNames, cwd)
     const service = ts.createLanguageService(serviceHost, registry)
 
     // Set the file contents into cache manually.
-    const updateMemoryCache = function (contents: string, fileName: string) {
+    const updateMemoryCache = (contents: string, fileName: string) => {
       const fileVersion = memoryCache.fileVersions.get(fileName) || 0
 
       // Avoid incrementing cache when nothing has changed.
@@ -348,7 +339,7 @@ export function register (opts: Options = {}): Register {
       memoryCache.fileContents.set(fileName, contents)
     }
 
-    getOutput = function (code: string, fileName: string, lineOffset: number = 0) {
+    getOutput = (code: string, fileName: string) => {
       updateMemoryCache(code, fileName)
 
       const output = service.getEmitOutput(fileName)
@@ -379,7 +370,7 @@ export function register (opts: Options = {}): Register {
       return [output.outputFiles[1].text, output.outputFiles[0].text]
     }
 
-    getTypeInfo = function (code: string, fileName: string, position: number) {
+    getTypeInfo = (code: string, fileName: string, position: number) => {
       updateMemoryCache(code, fileName)
 
       const info = service.getQuickInfoAtPosition(fileName, position)
@@ -388,10 +379,35 @@ export function register (opts: Options = {}): Register {
 
       return { name, comment }
     }
+  } else {
+    if (typeof transformers === 'function') {
+      throw new TypeError('Transformers function is unavailable in "--transpile-only"')
+    }
+
+    getOutput = (code: string, fileName: string): SourceOutput => {
+      const result = ts.transpileModule(code, {
+        fileName,
+        transformers,
+        compilerOptions: config.options,
+        reportDiagnostics: true
+      })
+
+      const diagnosticList = result.diagnostics ?
+        filterDiagnostics(result.diagnostics, ignoreDiagnostics) :
+        []
+
+      if (diagnosticList.length) reportTSError(configDiagnosticList)
+
+      return [result.outputText, result.sourceMapText as string]
+    }
+
+    getTypeInfo = () => {
+      throw new TypeError('Type information is unavailable in "--transpile-only"')
+    }
   }
 
   // Create a simple TypeScript compiler proxy.
-  function compile (code: string, fileName: string, lineOffset?: number) {
+  function compile (code: string, fileName: string, lineOffset = 0) {
     const [value, sourceMap] = getOutput(code, fileName, lineOffset)
     const output = updateOutput(value, fileName, sourceMap, getExtension)
     outputCache.set(fileName, output)
@@ -401,7 +417,7 @@ export function register (opts: Options = {}): Register {
   const register: Register = { cwd, compile, getTypeInfo, extensions, ts }
 
   // Register the extensions.
-  registerExtensions(opts, extensions, ignore, register, originalJsHandler)
+  registerExtensions(options.preferTsExts, extensions, ignore, register, originalJsHandler)
 
   return register
 }
@@ -430,7 +446,7 @@ function reorderRequireExtension (ext: string) {
  * Register the extensions to support when importing files.
  */
 function registerExtensions (
-  opts: Options,
+  preferTsExts: boolean | null | undefined,
   extensions: string[],
   ignore: RegExp[],
   register: Register,
@@ -441,7 +457,7 @@ function registerExtensions (
     registerExtension(ext, ignore, register, originalJsHandler)
   }
 
-  if (opts.preferTsExts) {
+  if (preferTsExts) {
     // tslint:disable-next-line
     const preferredExtensions = new Set([...extensions, ...Object.keys(require.extensions)])