Uncaught ReferenceError: π is not defined
An identifier must start with $, _, or any character in the Unicode categories “Uppercase letter (Lu)”, “Lowercase letter (Ll)”, “Titlecase letter (Lt)”, “Modifier letter (Lm)”, “Other letter (Lo)”, or “Letter number (Nl)”.
This allows us to write following code from ES5
var π = Math.PI;
Isn't this cool?