Add optional chaining, discussion on named imports

Author: dandv

.gitignore

@@ -0,0 +1,2 @@
+node_modules
+*.js

Lib.ts

@@ -1,5 +1,11 @@
 export class Lib {
-  run() {
-    console.log('Success!');
+  run(): void {
+    // Make sure optional chaining works - either by `tsc` transpiling it, or by node running it under a flag
+    const a = {
+      b: {
+        c: 'foo'
+      }
+    };
+    a.b?.c && console.log('Success!');
   }
 }

README.md

@@ -7,6 +7,8 @@ Minimalistic example of configuring TypeScript and Node to:
 * import your own modules without specifying an extension
 * run the resulting JavaScript code
 
+There is no need for Babel.
+
 # Emit ES modules code
 
 In `tsconfig.json`, set this in `compilerOptions`:
@@ -16,23 +18,42 @@ In `tsconfig.json`, set this in `compilerOptions`:
     "module": "esnext",  // Output `import`/`export` ES modules
 ```
 
+
 # Import modules that use Node built-ins (`http`, `url` etc.)
 
 * run `npm install --save-dev @types/node`
 * in `tsconfig.json` under `compilerOptions`, set
   * `"moduleResolution": "node"`, so `tsc` can find modules [when targeting ES6+](https://github.com/Microsoft/TypeScript/issues/8189) 
   * `"types": ["node"]` to avoid errors related to Node built-in modules  
 
+
 # Import modules that don't have named exports
 
-Set `"allowSyntheticDefaultImports": true` in `tsconfig.json`. In our code,
-instead of `import { InfluxDB } from 'influx` we have to write:
+Normally we could write in TypeScript
+
+    import { InfluxDB } from 'influx';
+
+but when generating ES modules code, that statement will be passed through as is, and will cause Node to fail with
+
+> SyntaxError: The requested module 'influx' does not provide an export named 'InfluxDB'
+
+because [`node-influx` doesn't provide named exports](https://github.com/node-influx/node-influx/issues/298) (and neither does an even more popular module, [`apollo-server`](https://github.com/apollographql/apollo-server/issues/1356#issuecomment-565277759)).
+
+One alternative would be to generate old ugly commonjs modules code by,
+
+* removing the `"type": "module"` line from `package.json`, and
+* changing the module line to `"module": "CommonJS"` in `tsconfig.json` (`allowSyntheticDefaultImports` also becomes unnecessary)
+
+Another is to import the entire module:
 
 ```js
 import Influx from 'influx';
 const influx = new Influx.InfluxDB();
 ```
 
+However, this will generate `Error TS1192: Module '...' has no default export.` To prevent that, set `"allowSyntheticDefaultImports": true` in `tsconfig.json`.
+
+
 # Import your own modules without specifying an extension
 
 When transpiling, [TypeScript won't generate an extension for you](https://github.com/microsoft/TypeScript/issues/16577). Run Node with the `node --experimental-specifier-resolution=node` parameter:
@@ -41,12 +62,16 @@ When transpiling, [TypeScript won't generate an extension for you](https://githu
 
 Otherwise, [node mandates that you specify the extension](https://nodejs.org/api/esm.html#esm_mandatory_file_extensions) in the `import` statement.
 
+To support optional chaining, add the `--harmony` flag to the node command line.
+
+
 # Run the resulting JavaScript code
 
 Add `"type": "module"` to `package.json`, because [TypeScript can't generate files with the .mjs extension](https://github.com/microsoft/TypeScript/issues/18442#issuecomment-581738714).
 
+
 # ESLint
 
-To be able to run `eslint`, we must create an `.eslintrc.cjs` file, rather than a `.js` one. Then, install the required dependencies:
+To be able to run `eslint`, we must create an `.eslintrc.cjs` file, rather than a `.js` one (due to `"type": "module"` in `package.json`). Then, install the required dependencies:
 
     npm i -D eslint @typescript-eslint/eslint-plugin @typescript-eslint/parser

package-lock.json

@@ -15,7 +15,8 @@
   "type": "module",
   "main": "run.js",
   "scripts": {
-    "start": "node --experimental-specifier-resolution=node run.js",
+    "build": "rm *.js && tsc",
+    "start": "node --experimental-specifier-resolution=node --harmony run.js",
     "lint": "eslint *.ts"
   },
   "dependencies": {
@@ -26,6 +27,6 @@
     "@typescript-eslint/eslint-plugin": "^2.19.0",
     "@typescript-eslint/parser": "^2.19.0",
     "eslint": "^6.8.0",
-    "typescript": "^3.7.5"
+    "typescript": "^3.8.3"
   }
 }

package.json

@@ -1,5 +1,13 @@
+// Import without specifying the extension. `./Lib.js` would look odd in a .ts file
 import { Lib } from './Lib';
+
+// Can't use named imports because https://github.com/node-influx/node-influx/issues/298
+// import { InfluxDB } from 'influx';
+// const influx = new InfluxDB();
+
 import Influx from 'influx';
 const influx = new Influx.InfluxDB();
+
 const l = new Lib();
 l.run();
+console.log(typeof influx);

run.ts

@@ -1,9 +1,10 @@
 {
   "compilerOptions": {
     "target": "esnext",
-    "module": "esnext",  // Output `import`/`export` ES modules
-    "moduleResolution": "node",  // Find modules in node_modules - https://github.com/Microsoft/TypeScript/issues/8189#issuecomment-212079251
-    "allowSyntheticDefaultImports": true,  // Allow default imports from modules with no default export. This does not affect code emit, just typechecking.
+    "module": "esnext",  // output `import`/`export` ES modules
+    //"module": "CommonJS",  // enables `import { InfluxDB } from 'influx'
+    "allowSyntheticDefaultImports": true,  // allow default imports from modules with no default export. This does not affect code emit, just typechecking.
+    "moduleResolution": "node",  // find modules in node_modules - https://github.com/Microsoft/TypeScript/issues/8189#issuecomment-212079251
     "types": ["node"]  // Influx uses built-in node modules like http or url
   }
 }