>>> | NN 2 IE 3 ECMA 1
This is the bitwise zero-fill right-shift operator. This operator shifts the bits of the first operand (to the right) by the number of columns specified by the second operand. With the bitwise right-shift operator (>>), new digits that fill in from the left end are 1s; with the zero-fill right-shift operator (>>>), the new digits at the left are zeros. Any digits that fall off the right end of the number are discarded. Microsoft also refers to this operator as the unsigned right-shift operator.
Example

    var shifted = 6 >>> 2;