Merge pull request #126 from iancmyers/rule-no-plusplus

Rule: no-plusplus

conf/eslint.json

@@ -21,6 +21,7 @@
         "no-new": 1,
         "no-new-func": 1,
         "no-native-reassign": 1,
+        "no-plusplus": 0,
         "no-delete-var": 1,
         "no-return-assign": 1,
 

docs/rules/README.md

@@ -51,5 +51,6 @@ These rules are purely matters of style and are quite subjective.
 
 The following rules are included for compatibility with [JSHint](http://jshint.com/) and [JSLint](http://jslint.com/). While the names of the rules may not match up with the JSHint/JSLint counterpart, the functionality is the same.
 
+* [no-plusplus] - disallow use of unary operators, `++` and `--` (off by default)
 * [no-bitwise] - disallow use of bitwise operators (off by default)
 * [guard-for-in] - make sure `for-in` loops have an `if` statement (off by default)

docs/rules/no-plusplus.js

@@ -0,0 +1,32 @@
+# no plusplus
+
+The `no-plusplus` rule flags the use of unary operators, `++` and `--`.
+
+```js
+var foo = 0;
+foo++;
+```
+
+## Rule Details
+
+This rule is aimed at flagging the use of `++` and `--`. Some believe that the use of these unary operators reduces code quality and clarity. There are some programming languages that completely exclude these operators.
+
+The following patterns are considered warnings:
+
+```js
+var foo = 0;
+foo++;
+
+var bar = 42;
+bar--;
+```
+
+The following patterns are not considered warnings:
+
+```js
+var foo = 0;
+foo += 1;
+
+var bar = 42;
+bar -= 1;
+```

lib/rules/no-plusplus.js

@@ -0,0 +1,20 @@
+/**
+ * @fileoverview Rule to flag use of unary increment and decrement operators.
+ * @author Ian Christian Myers
+ */
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = function(context) {
+
+    return {
+
+        "UpdateExpression": function(node) {
+            context.report(node, "Unary operator '" + node.operator + "' used.");
+        }
+
+    };
+
+};

tests/lib/rules/no-plusplus.js

@@ -0,0 +1,60 @@
+/**
+ * @fileoverview Tests for no-plusplus.
+ * @author Ian Christian Myers
+ */
+
+//------------------------------------------------------------------------------
+// Requirements
+//------------------------------------------------------------------------------
+
+var vows = require("vows"),
+    assert = require("assert"),
+    eslint = require("../../../lib/eslint");
+
+//------------------------------------------------------------------------------
+// Constants
+//------------------------------------------------------------------------------
+
+var RULE_ID = "no-plusplus";
+
+//------------------------------------------------------------------------------
+// Tests
+//------------------------------------------------------------------------------
+
+vows.describe(RULE_ID).addBatch({
+
+    "when evaluating unary increment operator": {
+
+        topic: "var foo = 0; foo++;",
+
+        "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, "Unary operator '++' used.");
+            assert.include(messages[0].node.type, "UpdateExpression");
+        }
+    },
+
+    "when evaluating unary decrement operator": {
+
+        topic: "var foo = 0; foo--;",
+
+        "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, 1);
+            assert.equal(messages[0].ruleId, RULE_ID);
+            assert.equal(messages[0].message, "Unary operator '--' used.");
+            assert.include(messages[0].node.type, "UpdateExpression");   
+        }
+    }
+
+}).export(module);