Add source map support

Author: dandv

README.md

@@ -99,3 +99,9 @@ Normally, to run Jest from `package.json`, we'd add a `"test": "jest"` line. Tha
 To pass parameters to Node when running Jest, we'll add the following `test` line:
 
     "test": "node --harmony node_modules/.bin/jest"
+
+
+# Source maps
+
+If your script generates an error, you'll see the line numbers from the generated `.js` files, which is not helpful. We want to see the original paths and line numbers from the `.ts` files. To do that, we'll add `sourceMap: true` to `tsconfig.json`, install [`source-map-support`](https://www.npmjs.com/package/source-map-support) and run node with the `-r source-map-support/register` parameter. Note that Jest already takes care of source mapping so you'll see the `.ts` line numbers without having to do anything extra.
+ 

package.json

@@ -16,7 +16,7 @@
   "main": "run.js",
   "scripts": {
     "build": "rm *.js && tsc",
-    "start": "node --experimental-specifier-resolution=node --harmony run.js",
+    "start": "node --experimental-specifier-resolution=node --harmony -r source-map-support/register run.js",
     "lint": "eslint *.ts",
     "test": "node --harmony node_modules/.bin/jest"
   },
@@ -32,6 +32,7 @@
     "eslint": "^6.8.0",
     "eslint-plugin-jest": "^23.8.2",
     "jest": "^25.2.3",
+    "source-map-support": "^0.5.16",
     "typescript": "^3.8.3"
   }
 }

run.ts

@@ -10,4 +10,12 @@ const influx = new Influx.InfluxDB();
 
 const l = new Lib();
 l.run();
-console.log('Should display "object":', typeof influx);
+
+try {
+  throw new Error('testing source mapping');
+} catch (e) {
+  if (e.stack.includes('.ts:')) {
+    console.info('Stack trace mapped back to TypeScript should indicate correct error line number');
+    console.info(e);
+  }
+}

test.ts

@@ -5,3 +5,12 @@ test('constructor', () => {
   const instance = new Lib();
   expect(instance instanceof Lib).toBeTruthy();
 });
+
+try {
+  throw new Error('testing source mapping in Jest');
+} catch (e) {
+  if (e.stack.includes('.ts:')) {
+    console.info('Stack trace mapped back to TypeScript should indicate correct error line number');
+    console.info(e);
+  }
+}

tsconfig.json

@@ -5,6 +5,7 @@
     //"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", "jest"]  // Influx uses built-in node modules like http or url
+    "types": ["node", "jest"],  // Influx uses built-in node modules like http or url
+    "sourceMap": true
   }
 }