use-isnan should only apply to comparison operators

src/rules/useIsnanRule.ts

@@ -45,7 +45,7 @@ export class Rule extends Lint.Rules.AbstractRule {
 class UseIsnanRuleWalker extends Lint.RuleWalker {
     protected visitBinaryExpression(node: ts.BinaryExpression): void {
         if ((this.isExpressionNaN(node.left) || this.isExpressionNaN(node.right))
-                && node.operatorToken.kind !== ts.SyntaxKind.EqualsToken) {
+                && this.isComparisonOperator(node.operatorToken.kind)) {
             this.addFailureAtNode(node, Rule.FAILURE_STRING + node.getText());
         }
         super.visitBinaryExpression(node);
@@ -54,4 +54,15 @@ class UseIsnanRuleWalker extends Lint.RuleWalker {
     private isExpressionNaN(node: ts.Node) {
         return node.kind === ts.SyntaxKind.Identifier && node.getText() === "NaN";
     }
+
+    private isComparisonOperator(operator: ts.BinaryOperator) {
+        return (operator === ts.SyntaxKind.LessThanToken
+            || operator === ts.SyntaxKind.GreaterThanToken
+            || operator === ts.SyntaxKind.LessThanEqualsToken
+            || operator === ts.SyntaxKind.GreaterThanEqualsToken
+            || operator === ts.SyntaxKind.EqualsEqualsToken
+            || operator === ts.SyntaxKind.ExclamationEqualsToken
+            || operator === ts.SyntaxKind.EqualsEqualsEqualsToken
+            || operator === ts.SyntaxKind.ExclamationEqualsEqualsToken);
+    }
 }

test/rules/use-isnan/test.ts.lint

@@ -9,6 +9,39 @@ if (isNaN(something)) { }
 // no violation for assignments
 let x = 0;
 x = NaN;
+x += NaN;
+x -= NaN;
+x /= NaN;
+x *= NaN;
+x %= NaN;
+x **= NaN;
+x <<= NaN;
+x >>= NaN;
+x >>>= NaN;
+x &= NaN;
+x ^= NaN;
+x |= NaN;
+
+// no violation for arithmetic operators
+x = x + NaN;
+x = NaN - x;
+x = x / NaN;
+x = NaN * x;
+x = x % NaN;
+x = NaN ** x;
+
+// no violation for bitwise operators
+x = x & NaN;
+x = NaN | x;
+x = x ^ NaN;
+x = NaN << x;
+x = x >> NaN;
+x = NaN >>> x;
+x = x & NaN;
+
+// no violation for other operators
+if (x instanceof NaN) { }
+if (NaN in x) { }
 
 // do not use equality operators to compare for NaN
 if (foo == NaN) {  }