upgrades core to 8.4.2

core/scripts/js/check.js

@@ -0,0 +1,23 @@
+const chalk = require('chalk');
+const fs = require('fs');
+const log = require('./log');
+const compile = require('./compile');
+
+module.exports = (filePath) => {
+  log(`'${filePath}' is being checked.`);
+  // Transform the file.
+  compile(filePath, function check(code) {
+    const fileName = filePath.slice(0, -7);
+    fs.readFile(`${fileName}.js`, function read(err, data) {
+      if (err) {
+        log(chalk.red(err));
+        process.exitCode = 1;
+        return;
+      }
+      if (code !== data.toString()) {
+        log(chalk.red(`'${filePath}' is not updated.`));
+        process.exitCode = 1;
+      }
+    });
+  });
+}