fix(betterer 🐛): make typescript properly optional

.betterer.ts

@@ -1,4 +1,3 @@
-import { eslint } from '@betterer/eslint';
 import { regexp } from '@betterer/regexp';
 
 export default {

README.md

@@ -17,13 +17,11 @@ npx @betterer/cli init
 To do it yourself, run the following from the root of your project:
 
 ```bash
-npm install @betterer/cli typescript --save-dev
+npm install @betterer/cli --save-dev
 ```
 
 You'll then need to make your own test file and test commands.
 
-_Note: Typescript is required to execute the `betterer` command. Your code does not have to be written in TS to use Betterer! Referencing it as a peer dependency helps to prevent unexpected behavior._
-
 ---
 
 ## Why?

packages/betterer/package.json

@@ -44,6 +44,9 @@
     "ts-node": "^9.0.0",
     "tslib": "^2.0.3"
   },
+  "optionalDependencies": {
+    "typescript": ">=2.7"
+  },
   "devDependencies": {
     "@types/callsite": "^1.0.30",
     "@types/prettier": "^1.12.0"

packages/betterer/src/register.ts

@@ -1,4 +1,4 @@
-import { RegisterOptions, register } from 'ts-node';
+import type { RegisterOptions } from 'ts-node';
 
 import { BettererConfig } from './config';
 
@@ -9,7 +9,7 @@ export const TS_EXTENSION = '.ts';
 type Extensions = typeof require.extensions;
 
 let isRegistered = false;
-export function registerExtensions(config: BettererConfig): void {
+export async function registerExtensions(config: BettererConfig): Promise<void> {
   if (isRegistered) {
     return;
   }
@@ -23,21 +23,34 @@ export function registerExtensions(config: BettererConfig): void {
   const JS = EXTENSIONS[JS_EXTENSION];
 
   if (!EXTENSIONS[TS_EXTENSION]) {
-    // Use TS-Node register to allow `.betterer.ts` config files:
-    const tsRegisterOptions: RegisterOptions = {
-      transpileOnly: true,
-      compilerOptions: {
-        module: 'commonjs'
-      }
-    };
-    if (config.tsconfigPath) {
-      tsRegisterOptions.project = config.tsconfigPath;
-    }
-    register(tsRegisterOptions);
+    await registerTypeScript(config);
   }
 
   // Force `.betterer.results` files to be loaded as JS:
   EXTENSIONS[RESULTS_EXTENTION] = (m: NodeModule, filePath: string): void => {
     JS(m, filePath);
   };
 }
+
+async function registerTypeScript(config: BettererConfig): Promise<void> {
+  let tsNode: typeof import('ts-node');
+  try {
+    await import('typescript');
+    tsNode = await import('ts-node');
+  } catch {
+    // Environment doesn't have TypeScript available, move on!
+    return;
+  }
+
+  // Use TS-Node register to allow `.betterer.ts` config files:
+  const tsRegisterOptions: RegisterOptions = {
+    transpileOnly: true,
+    compilerOptions: {
+      module: 'commonjs'
+    }
+  };
+  if (config.tsconfigPath) {
+    tsRegisterOptions.project = config.tsconfigPath;
+  }
+  tsNode.register(tsRegisterOptions);
+}

packages/betterer/src/runner/runner.ts

@@ -21,7 +21,7 @@ export class BettererRunnerΩ implements BettererRunner {
     let reporter = loadReporters([DEFAULT_REPORTER]);
     try {
       config = await createConfig(partialConfig);
-      registerExtensions(config);
+      await registerExtensions(config);
       if (config.silent) {
         reporter = loadReporters([]);
       }

yarn.lock

@@ -9280,7 +9280,7 @@ typedarray@^0.0.6:
   resolved "https://registry.npmjs.org/typedarray/-/typedarray-0.0.6.tgz#867ac74e3864187b1d3d47d996a78ec5c8830777"
   integrity sha1-hnrHTjhkGHsdPUfZlqeOxciDB3c=
 
-typescript@^4.1.3:
+typescript@>=2.7, typescript@^4.1.3:
   version "4.1.5"
   resolved "https://registry.npmjs.org/typescript/-/typescript-4.1.5.tgz#123a3b214aaff3be32926f0d8f1f6e704eb89a72"
   integrity sha512-6OSu9PTIzmn9TCDiovULTnET6BgXtDYL4Gg4szY+cGsc3JP1dQL8qvE8kShTRx1NIw4Q9IBHlwODjkjWEtMUyA==