The ECMAScript specification states that the value is converted to UInt32 in step 5 and 8 of http://www.ecma-international.org/ecma-262/5.1/#sec-11.7:
11.7.3 The Unsigned Right Shift Operator ( >>> )
Performs a zero-filling bitwise right shift operation on the left operand by the amount > specified by the right operand.
The production
ShiftExpression : ShiftExpression >>> AdditiveExpression
is evaluated as follows:
- Let
lref
be the result of evaluatingShiftExpression
.- Let
lval
beGetValue(lref)
.- Let
rref
be the result of evaluatingAdditiveExpression
.- Let
rval
beGetValue(rref)
.- Let
lnum
beToUint32(lval)
.- Let
rnum
beToUint32(rval)
.- Let
shiftCount
be the result of masking out all but the least significant 5 bits ofrnum
, that is, computernum & 0x1F
.- Return the result of performing a zero-filling right shift of
lnum
byshiftCount
bits. Vacated bits are filled with zero. The result is an unsigned 32-bit integer.