QL code and tests for C#/C++/JavaScript.

javascript/ql/src/React/examples/UnusedOrUndefinedStateProperty.js

@@ -0,0 +1,16 @@
+class Clock extends React.Component {
+    constructor(props) {
+        super(props);
+        this.state = { };
+    }
+
+    render() {
+         // BAD: this.state.date is undefined
+        var now = this.state.date.toLocaleTimeString();
+        return (
+                <div>
+                <h2>The time is {now}.</h2>
+                </div>
+        );
+    }
+}