TypeScript - Intellisense support for ES modules (_.mjs_ files)

readme.md

TypeScript - Intellisense support for ES modules

This patch, based on commit https://github.com/Microsoft/TypeScript/commit/beebda3574be7f9a51f33ac24ab117f696ca9055, will add Intellisense support to projects which utilise the .mjs file extension for JavaScript modules.

⚠️ Warning

• I have only used this from within tsserver. I did not attempt to use the tsc tool to do any kind of compilation of .mjs files.
• This patch causes tsserver to treat all .mjs files as regular JavaScript files. This might be semantically wrong since these files have different semantics.

What works

• Import statements which refer to .mjs modules without extension
• Intellisense for things declared in .mjs files

Usage

• Clone the TypeScript repository
• Download this patch file
• Apply the patch on top of master (if it does not apply, checkout the base commit mentioned above and apply it on top of that instead): `cat tsserver-intellisense.patch | git am
• Compile the TypeScript binaries: npm install && npx jake local
• Point your IDE/other tool to TypeScript/built/local/tsserver.js to use the locally-built TypeScript server
• Profit 🎉

tsserver-intellisense.patch

From 6429aacce7611a236c559083ccd563259cbe64ca Mon Sep 17 00:00:00 2001
From: Robert Rossmann <rr.rossmann@me.com>
Date: Mon, 31 Dec 2018 18:29:45 +0100
Subject: [PATCH] Add intellisense support for .mjs files via tsserver

---
 src/compiler/moduleNameResolver.ts | 2 +-
 src/compiler/moduleSpecifiers.ts   | 1 +
 src/compiler/program.ts            | 1 +
 src/compiler/types.ts              | 1 +
 src/compiler/utilities.ts          | 7 ++++---
 src/services/stringCompletions.ts  | 1 +
 src/services/types.ts              | 1 +
 7 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/src/compiler/moduleNameResolver.ts b/src/compiler/moduleNameResolver.ts
index b8aa9fa2..7c6f9de6 100644
--- a/src/compiler/moduleNameResolver.ts
+++ b/src/compiler/moduleNameResolver.ts
@@ -1071,7 +1071,7 @@ namespace ts {
             case Extensions.TypeScript:
                 return tryExtension(Extension.Ts) || tryExtension(Extension.Tsx) || tryExtension(Extension.Dts);
             case Extensions.JavaScript:
-                return tryExtension(Extension.Js) || tryExtension(Extension.Jsx);
+                return tryExtension(Extension.Mjs) || tryExtension(Extension.Js) || tryExtension(Extension.Jsx);
             case Extensions.TSConfig:
             case Extensions.Json:
                 return tryExtension(Extension.Json);
diff --git a/src/compiler/moduleSpecifiers.ts b/src/compiler/moduleSpecifiers.ts
index f5bac45f..14ac7bbe 100644
--- a/src/compiler/moduleSpecifiers.ts
+++ b/src/compiler/moduleSpecifiers.ts
@@ -433,6 +433,7 @@ namespace ts.moduleSpecifiers {
                 return Extension.Js;
             case Extension.Tsx:
                 return options.jsx === JsxEmit.Preserve ? Extension.Jsx : Extension.Js;
+            case Extension.Mjs:
             case Extension.Js:
             case Extension.Jsx:
             case Extension.Json:
diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index 080b17b8..3f0a3111 100644
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -3152,6 +3152,7 @@ namespace ts {
                 return needJsx();
             case Extension.Jsx:
                 return needJsx() || needAllowJs();
+            case Extension.Mjs:
             case Extension.Js:
                 return needAllowJs();
             case Extension.Json:
diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index 6e2e4805..5ed67ae5 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -4962,6 +4962,7 @@ namespace ts {
         Tsx = ".tsx",
         Dts = ".d.ts",
         Js = ".js",
+        Mjs = ".mjs",
         Jsx = ".jsx",
         Json = ".json"
     }
diff --git a/src/compiler/utilities.ts b/src/compiler/utilities.ts
index 23c92216..1cceb159 100644
--- a/src/compiler/utilities.ts
+++ b/src/compiler/utilities.ts
@@ -8124,6 +8124,7 @@ namespace ts {
     export function getScriptKindFromFileName(fileName: string): ScriptKind {
         const ext = fileName.substr(fileName.lastIndexOf("."));
         switch (ext.toLowerCase()) {
+            case Extension.Mjs:
             case Extension.Js:
                 return ScriptKind.JS;
             case Extension.Jsx:
@@ -8146,8 +8147,8 @@ namespace ts {
     export const supportedTSExtensionsWithJson: ReadonlyArray<Extension> = [Extension.Ts, Extension.Tsx, Extension.Dts, Extension.Json];
     /** Must have ".d.ts" first because if ".ts" goes first, that will be detected as the extension instead of ".d.ts". */
     export const supportedTSExtensionsForExtractExtension: ReadonlyArray<Extension> = [Extension.Dts, Extension.Ts, Extension.Tsx];
-    export const supportedJSExtensions: ReadonlyArray<Extension> = [Extension.Js, Extension.Jsx];
-    export const supportedJSAndJsonExtensions: ReadonlyArray<Extension> = [Extension.Js, Extension.Jsx, Extension.Json];
+    export const supportedJSExtensions: ReadonlyArray<Extension> = [Extension.Mjs, Extension.Js, Extension.Jsx];
+    export const supportedJSAndJsonExtensions: ReadonlyArray<Extension> = [Extension.Mjs, Extension.Js, Extension.Jsx, Extension.Json];
     const allSupportedExtensions: ReadonlyArray<Extension> = [...supportedTSExtensions, ...supportedJSExtensions];
     const allSupportedExtensionsWithJson: ReadonlyArray<Extension> = [...supportedTSExtensions, ...supportedJSExtensions, Extension.Json];
 
@@ -8255,7 +8256,7 @@ namespace ts {
         }
     }
 
-    const extensionsToRemove = [Extension.Dts, Extension.Ts, Extension.Js, Extension.Tsx, Extension.Jsx, Extension.Json];
+    const extensionsToRemove = [Extension.Dts, Extension.Ts, Extension.Mjs, Extension.Js, Extension.Tsx, Extension.Jsx, Extension.Json];
     export function removeFileExtension(path: string): string {
         for (const ext of extensionsToRemove) {
             const extensionless = tryRemoveExtension(path, ext);
diff --git a/src/services/stringCompletions.ts b/src/services/stringCompletions.ts
index 9548397a..d449b66c 100644
--- a/src/services/stringCompletions.ts
+++ b/src/services/stringCompletions.ts
@@ -66,6 +66,7 @@ namespace ts.Completions.StringCompletions {
     function kindModifiersFromExtension(extension: Extension | undefined): ScriptElementKindModifier {
         switch (extension) {
             case Extension.Dts: return ScriptElementKindModifier.dtsModifier;
+            case Extension.Mjs: return ScriptElementKindModifier.mjsModifier;
             case Extension.Js: return ScriptElementKindModifier.jsModifier;
             case Extension.Json: return ScriptElementKindModifier.jsonModifier;
             case Extension.Jsx: return ScriptElementKindModifier.jsxModifier;
diff --git a/src/services/types.ts b/src/services/types.ts
index 5100a999..6582dfd4 100644
--- a/src/services/types.ts
+++ b/src/services/types.ts
@@ -1138,6 +1138,7 @@ namespace ts {
         dtsModifier = ".d.ts",
         tsModifier = ".ts",
         tsxModifier = ".tsx",
+        mjsModifier = ".mjs",
         jsModifier = ".js",
         jsxModifier = ".jsx",
         jsonModifier = ".json",
-- 
2.20.0