taintEnabled aborts JavaScript in Safari Browser beta

This page contains the following three lines of JavaScript code: 

document.write("Line of text before the taintEnabled method"); 
document.write("navigator.taintEnabled() = " + navigator.taintEnabled() + ""); 
document.write("Line of text after the taintEnabled method");

Each line should appear in the box below, even if the command is not recognized.  However, in the beta version of Apple's Safari browser the middle line does not appear and nothing after it in the JavaScript code works either.

Here is the display for your browser: