Use a script for formatting

Author: pelotom

Diff for: package.json

@@ -9,7 +9,7 @@
   "types": "./lib/index.d.ts",
   "scripts": {
     "build": "tsc --pretty",
-    "format": "prettier $([ \"$CI\" == true ] && echo --list-different || echo --write) './**/*.{ts,tsx,js,json,css}'",
+    "format": "node scripts/format.js",
     "test": "jest --no-cache --verbose --coverage",
     "test:watch": "jest --watch"
   },
@@ -34,4 +34,4 @@
     "mapCoverage": true,
     "testEnvironment": "node"
   }
-}
+}

Diff for: scripts/format.js

@@ -0,0 +1,25 @@
+'use strict';
+
+// Makes the script crash on unhandled rejections instead of silently
+// ignoring them. In the future, promise rejections that are not handled will
+// terminate the Node.js process with a non-zero exit code.
+process.on('unhandledRejection', err => {
+  throw err;
+});
+
+const { exec } = require('child_process');
+
+const command = [
+  '$(npm bin)/prettier',
+  process.env.CI ? '--list-different' : '--write',
+  '"./**/*.{ts,tsx,js,json,css}"',
+];
+
+exec(command.join(' '), (error, stdout) => {
+  if (error) {
+    console.error('Found formatting issues in:\n');
+    console.error(stdout);
+    console.error('Looks like someone forgot to run `yarn format` before pushing 😱');
+    process.exit(1);
+  }
+});