var len = t.length >>> 0;
>>>operator is the bit-shift operator. It causes a binary right-shift of the bits that make up it's target, by the number of bits passed in the operand. This is something you normally would only use in clever or low-level programming. I don't think I've used bit-shift operators since I was writing a device driver in C about 15 years ago.
So why would you apply a zero operand? Wouldn't that do nothing? What's this all about?
len is a valid number - if
t.length exists, is numeric, and is integral. If it's already good, it will be unaffected by the operation. If it's undefined or non-numeric, it will always return zero. Basically, it's shorthand for something like:
parseInt(t.length) || 0
Clever. Learn something new every day.