Add typeof-compare rule

docs/_data/rules.json

@@ -1557,6 +1557,15 @@
     "type": "typescript",
     "typescriptOnly": true
   },
+  {
+    "ruleName": "typeof-compare",
+    "description": "Makes sure result of `typeof` is compared to correct string values",
+    "optionsDescription": "",
+    "options": {},
+    "optionExamples": [],
+    "type": "functionality",
+    "typescriptOnly": false
+  },
   {
     "ruleName": "use-isnan",
     "description": "Enforces use of the `isNaN()` function to check for NaN references instead of a comparison to the `NaN` constant.",

docs/rules/typeof-compare/index.html

@@ -0,0 +1,12 @@
+---
+ruleName: typeof-compare
+description: Makes sure result of `typeof` is compared to correct string values
+optionsDescription: ''
+options: {}
+optionExamples: []
+type: functionality
+typescriptOnly: false
+layout: rule
+title: 'Rule: typeof-compare'
+optionsJSON: '{}'
+---

src/rules/typeofCompareRule.ts

@@ -0,0 +1,96 @@
+/**
+ * @license
+ * Copyright 2013 Palantir Technologies, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import * as ts from "typescript";
+
+import * as Lint from "../index";
+
+export class Rule extends Lint.Rules.AbstractRule {
+    /* tslint:disable:object-literal-sort-keys */
+    public static metadata: Lint.IRuleMetadata = {
+        ruleName: "typeof-compare",
+        description: "Makes sure result of `typeof` is compared to correct string values",
+        optionsDescription: "",
+        options: {},
+        optionExamples: [],
+        type: "functionality",
+        typescriptOnly: false,
+    };
+    /* tslint:enable:object-literal-sort-keys */
+
+    public static FAILURE_STRING = "typeof must be compared to correct value";
+
+    public apply(sourceFile: ts.SourceFile): Lint.RuleFailure[] {
+        const comparisonWalker = new ComparisonWalker(sourceFile, this.getOptions());
+        return this.applyWithWalker(comparisonWalker);
+    }
+}
+
+class ComparisonWalker extends Lint.RuleWalker {
+    private static LEGAL_TYPEOF_RESULTS = ["undefined", "string", "boolean", "number", "function", "object", "symbol"];
+
+    private static isCompareOperator(node: ts.Node): boolean {
+        return node.kind === ts.SyntaxKind.EqualsEqualsToken || node.kind === ts.SyntaxKind.EqualsEqualsEqualsToken;
+    }
+
+    private static isLegalStringLiteral(node: ts.Node) {
+        return ComparisonWalker.LEGAL_TYPEOF_RESULTS.indexOf(node.getText()) > -1;
+    }
+
+    private static isFaultyOtherSideOfTypeof(node: ts.Node): boolean {
+        switch (node.kind) {
+            case ts.SyntaxKind.StringLiteral:
+                if (!ComparisonWalker.isLegalStringLiteral(node)) {
+                    return true;
+                }
+                break;
+            case ts.SyntaxKind.Identifier:
+                if ((<ts.Identifier> node).originalKeywordKind === ts.SyntaxKind.UndefinedKeyword) {
+                    return true;
+                }
+                break;
+            case ts.SyntaxKind.NullKeyword:
+            case ts.SyntaxKind.FirstLiteralToken:
+            case ts.SyntaxKind.TrueKeyword:
+            case ts.SyntaxKind.FalseKeyword:
+            case ts.SyntaxKind.ObjectLiteralExpression:
+            case ts.SyntaxKind.ArrayLiteralExpression:
+                return true;
+            default: break;
+        }
+        return false;
+    }
+
+    public visitBinaryExpression(node: ts.BinaryExpression) {
+        let isFaulty = false;
+        if (ComparisonWalker.isCompareOperator(node.operatorToken)) {
+            // typeof is at left
+            if (node.left.kind === ts.SyntaxKind.TypeOfExpression && ComparisonWalker.isFaultyOtherSideOfTypeof(node.right)) {
+                isFaulty = true;
+            }
+            // typeof is at right
+            if (node.right.kind === ts.SyntaxKind.TypeOfExpression && ComparisonWalker.isFaultyOtherSideOfTypeof(node.left)) {
+                isFaulty = true;
+            }
+        }
+        if (isFaulty) {
+            this.addFailure(this.createFailure(node.getStart(), node.getWidth(), Rule.FAILURE_STRING));
+        }
+        super.visitBinaryExpression(node);
+    }
+
+}

test/rules/typeof-compare/test.js.lint

@@ -0,0 +1,38 @@
+var testVariable = 123;
+
+function testFunction() {
+    if (typeof x === 'null') {
+        ~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+        console.log("called");
+    }
+    const x = typeof foo === 'undefied'
+              ~~~~~~~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+}
+
+console.log(typeof window == 'object ')
+            ~~~~~~~~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+
+const string = "string";
+typeof bar === string
+
+typeof bar === 123
+~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+typeof bar === undefined
+~~~~~~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+typeof bar === null
+~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+typeof bar === true
+~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+typeof bar === false
+~~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+
+123 === typeof bar
+~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+undefined === typeof bar
+~~~~~~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+null === typeof bar
+~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+true === typeof bar
+~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+false === typeof bar
+~~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]

test/rules/typeof-compare/test.ts.lint

@@ -0,0 +1,38 @@
+var testVariable = 123;
+
+function testFunction() {
+    if (typeof x === 'null') {
+        ~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+        console.log("called");
+    }
+    const x = typeof foo === 'undefied'
+              ~~~~~~~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+}
+
+console.log(typeof window == 'object ')
+            ~~~~~~~~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+
+const string = "string";
+typeof bar === string
+
+typeof bar === 123
+~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+typeof bar === undefined
+~~~~~~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+typeof bar === null
+~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+typeof bar === true
+~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+typeof bar === false
+~~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+
+123 === typeof bar
+~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+undefined === typeof bar
+~~~~~~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+null === typeof bar
+~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+true === typeof bar
+~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+false === typeof bar
+~~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]

test/rules/typeof-compare/tslint.json

@@ -0,0 +1,8 @@
+{
+  "rules": {
+    "typeof-compare": true
+  },
+  "jsRules": {
+    "typeof-compare": true
+  }
+}