Add typeof-compare rule

src/rules/typeofCompareRule.ts

@@ -0,0 +1,76 @@
+/**
+ * @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;
+    }
+
+    public visitBinaryExpression(node: ts.BinaryExpression) {
+        if (ComparisonWalker.isCompareOperator(node.operatorToken)) {
+            // typeof is at left
+            if (node.left.kind === ts.SyntaxKind.TypeOfExpression) {
+                if (node.right.kind !== ts.SyntaxKind.StringLiteral) {
+                    this.addFailure(this.createFailure(node.getStart(), node.getWidth(), Rule.FAILURE_STRING));
+                } else if (!ComparisonWalker.isLegalStringLiteral(node.right)) {
+                    this.addFailure(this.createFailure(node.getStart(), node.getWidth(), Rule.FAILURE_STRING));
+                }
+            }
+            // typeof is at right
+            if (node.right.kind === ts.SyntaxKind.TypeOfExpression) {
+                if (node.left.kind !== ts.SyntaxKind.StringLiteral) {
+                    this.addFailure(this.createFailure(node.getStart(), node.getWidth(), Rule.FAILURE_STRING));
+                } else if (!ComparisonWalker.isLegalStringLiteral(node.left)) {
+                    this.addFailure(this.createFailure(node.getStart(), node.getWidth(), Rule.FAILURE_STRING));
+                }
+            }
+        }
+        super.visitBinaryExpression(node);
+    }
+
+}

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

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+var testVariable = 123;
+
+function testFunction() {
+    if (typeof x === 'null') {
+        ~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+        console.log("called");
+    }
+    var x = typeof foo === 'undefied'
+            ~~~~~~~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+}
+
+console.log(typeof window == 'object ')
+            ~~~~~~~~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+
+var a = typeof foo === null
+        ~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+
+var bar = typeof baz == testFunction;
+          ~~~~~~~~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]

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

@@ -0,0 +1,19 @@
+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]
+
+var a = typeof foo === null
+        ~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]
+
+var bar = typeof baz == testFunction;
+          ~~~~~~~~~~~~~~~~~~~~~~~~~~      [typeof must be compared to correct value]

test/rules/typeof-compare/tslint.json

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+{
+  "rules": {
+    "typeof-compare": true
+  },
+  "jsRules": {
+    "typeof-compare": true
+  }
+}