Hack to convert javascript number to UInt32

Question

Edit: This question is out of date as the Polyfill example has been updated. I\'m leaving the question here just for reference. Read the correct answer for usef

Answer 1

The result is, indeed, converted back to a number, i.e., a 64-bit precision floating point number. However, before it is converted back, both operands are converted to UInt32, then the right shift operation is performed. This is specified in ECMAScript here: http://www.ecma-international.org/ecma-262/5.1/#sec-11.7.3

The net result of length >>> 0 is therefore, because >>> 0 itself is a no-op, to convert length to a UInt32 then back to a double. What is it good for? It forces the loss of precision, and effectively forces the value to be 1) and integer and 2) in the range [0, 2^32-1]. For example, if it was -1, it will become 2^32-1 == 4294967295. If it was, 3.6, it will become 3.