Merge pull request eslint#79 from ilyavolodin/no-new

Rule: Do not use 'new' for side effects

conf/eslint.json

@@ -14,6 +14,7 @@
         "no-undef-init": 1,
         "no-octal": 1,
         "no-new-wrappers": 1,
+        "no-new": 1,
 
         "smarter-eqeqeq": 0,
         "camelcase": 1,

docs/Rules.md

@@ -24,6 +24,7 @@ These are rules designed to prevent you from making mistakes. They either prescr
 * [no-undef-init] - disallow use of undefined when initializing variables
 * [no-floating-decimal] - disallow the use of leading or trailing decimal points in numeric literals
 * [no-octal] - disallow use of octal literals
+* [no-new] - disallow use of new operator when not part of the assignment or comparison
 
 ## Stylistic Issues
 

lib/rules/no-new.js

@@ -0,0 +1,23 @@
+/**
+ * @fileoverview Rule to flag statements with function invocation preceded by
+ * "new" and not part of assignment
+ * @author Ilya Volodin
+ */
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = function(context) {
+
+    return {
+
+        "ExpressionStatement": function(node) {
+
+            if (node.expression.type === "NewExpression") {
+                context.report(node, "Do not use 'new' for side effects");
+            }
+        }
+    };
+
+};

tests/lib/rules/no-new.js

@@ -0,0 +1,72 @@
+/**
+ * @fileoverview Tests for no-new rule.
+ * @author Ilya Volodin
+ */
+
+//------------------------------------------------------------------------------
+// Requirements
+//------------------------------------------------------------------------------
+
+var vows = require("vows"),
+    assert = require("assert"),
+    eslint = require("../../../lib/eslint");
+
+//------------------------------------------------------------------------------
+// Constants
+//------------------------------------------------------------------------------
+
+var RULE_ID = "no-new";
+
+//------------------------------------------------------------------------------
+// Tests
+//------------------------------------------------------------------------------
+
+vows.describe(RULE_ID).addBatch({
+
+    "when evaluating 'new Date()": {
+
+        topic: "new Date()",
+
+        "should report a violation": function(topic) {
+            var config = { rules: {} };
+            config.rules[RULE_ID] = 1;
+
+            var messages = eslint.verify(topic, config);
+
+            assert.equal(messages.length, 1);
+            assert.equal(messages[0].ruleId, RULE_ID);
+            assert.equal(messages[0].message, "Do not use 'new' for side effects");
+            assert.include(messages[0].node.type, "ExpressionStatement");
+        }
+    },
+
+    "when evaluating 'var a = new Date()": {
+
+        topic: "var a = new Date()",
+
+        "should not report a violation": function(topic) {
+            var config = { rules: {} };
+            config.rules[RULE_ID] = 1;
+
+            var messages = eslint.verify(topic, config);
+
+            assert.equal(messages.length, 0);
+        }
+    },
+
+    "when evaluating 'var a; if (a === new Date()) { a=false; }": {
+
+        topic: "var a; if (a === new Date()) { a = false; }",
+
+        "should not report a violation": function(topic) {
+            var config = { rules: {} };
+            config.rules[RULE_ID] = 1;
+
+            var messages = eslint.verify(topic, config);
+
+            assert.equal(messages.length, 0);
+        }
+    }
+
+
+}).export(module);