x
 
<!DOCTYPE html>
<html>
<body>
<h2>Global "use strict" declaration.</h2>
<p>Activate debugging in your browser (F12) to see the error report.</p>
<script>
"use strict";
myFunction();
function myFunction() {
  y = 3.14;   // This will cause an error (y is not defined)
}
</script>
</body>
</html>