Add undef-init rule (with yo eslint:rule) and tests for it

lib/ruleNameMessageMap.js

@@ -0,0 +1,3 @@
+module.exports = {
+    'undef-init': "Always initialize variables during declaration. Set it explicitly to undefined, if required.",
+}

lib/rules/undef-init.js

@@ -0,0 +1,60 @@
+/**
+ * @fileoverview Always initialize variables during declaration. Set it explicitly to undefined, if required.
+ * @author Abhas Bhattacharya
+ */
+"use strict";
+
+const ruleMessage = require('../ruleNameMessageMap')['undef-init'];
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = {
+    meta: {
+        docs: {
+            description: ruleMessage,
+            category: "Fill me in",
+            recommended: false
+        },
+        fixable: "code",
+        schema: [
+        ]
+    },
+
+    create: function (context) {
+
+        // variables should be defined here
+        const defaultAllowInForConditon = {
+            ForInStatement: true,
+            ForOfStatement: true,
+        }
+
+        //----------------------------------------------------------------------
+        // Public
+        //----------------------------------------------------------------------
+
+        return {
+            "VariableDeclarator": function (node) {
+
+                if (node.init === null) {
+                    // Parent in always VariableDeclarator, whose parent can be directly one of the for in / for of statements
+                    if (node.parent.parent.type === 'ForInStatement' && defaultAllowInForConditon.ForInStatement) {
+                        return;
+                    }
+                    if (node.parent.parent.type === 'ForOfStatement' && defaultAllowInForConditon.ForOfStatement) {
+                        return;
+                    }
+
+                    context.report({
+                        node:node, 
+                        message:ruleMessage,
+                        fix: function(fixer) {
+                            return fixer.insertTextAfter(node, " = undefined");
+                        }
+                    });
+                }
+            }
+        };
+    }
+};