kriskowal/es5-shim — comment on commit 05f463d574519ade5d56fb58d640de3b401adf7c
File: tests/helpers/h-kill.js line 20
By jdalton:

Ya JSC and V8 will restore native methods on prototypes if you `delete` custom additions too...

~~~ js
Array.prototype.push = 1;
typeof [].push; // number
delete Array.prototype.push;
typeof [].push // function
~~~

Safari < 5 and Chrome cannot restore methods on the Object.prototype.