From 5f92d28e5299a59e120a993bfd4c74dc4ec3a6c6 Mon Sep 17 00:00:00 2001
From: Andrew Clark <acdlite@fb.com>
Date: Tue, 28 Feb 2017 13:04:33 -0800
Subject: [PATCH] New ESLint rule that warns against Boolean and String
 constructors

---
 .eslintrc.js                                  |  1 +
 .../boolean-and-string-constructors.js        | 35 +++++++++++++++++++
 eslint-rules/index.js                         |  1 +
 3 files changed, 37 insertions(+)
 create mode 100644 eslint-rules/boolean-and-string-constructors.js

diff --git a/.eslintrc.js b/.eslintrc.js
index fda855f401..7f42585cf2 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -55,6 +55,7 @@ module.exports = {
     // CUSTOM RULES
     // the second argument of warning/invariant should be a literal string
     'react-internal/warning-and-invariant-args': ERROR,
+    'react-internal/boolean-and-string-constructors': ERROR,
   },
 
   globals: {
diff --git a/eslint-rules/boolean-and-string-constructors.js b/eslint-rules/boolean-and-string-constructors.js
new file mode 100644
index 0000000000..fcf13c2ccf
--- /dev/null
+++ b/eslint-rules/boolean-and-string-constructors.js
@@ -0,0 +1,35 @@
+/**
+ * Copyright 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @emails react-core
+*/
+
+'use strict';
+
+module.exports = function(context) {
+  function check(node) {
+    const name = node.callee.name;
+    let msg = null;
+    switch (name) {
+      case 'Boolean':
+        msg = 'To cast a value to a boolean, use double negation: !!value';
+        break;
+      case 'String':
+        msg = 'To cast a value to a string, concat it with the empty string: \'\' + value';
+        break;
+    }
+    if (msg) {
+      context.report(node, `Do not use the ${name} constructor. ${msg}`);
+    }
+  }
+
+  return {
+    CallExpression: check,
+    NewExpression: check,
+  };
+};
diff --git a/eslint-rules/index.js b/eslint-rules/index.js
index 5efee2d47c..accd0e675c 100644
--- a/eslint-rules/index.js
+++ b/eslint-rules/index.js
@@ -3,5 +3,6 @@
 module.exports = {
   rules: {
     'warning-and-invariant-args': require('./warning-and-invariant-args'),
+    'boolean-and-string-constructors': require('./boolean-and-string-constructors'),
   },
 };