Count number of 1's in binary representation

Question

Efficient way to count number of 1s in the binary representation of a number in O(1) if you have enough memory to play with. This is an interview question I found on an onli

Answer 1

The best way in javascript to do so is

function getBinaryValue(num){
 return num.toString(2);
}

function checkOnces(binaryValue){
    return binaryValue.toString().replace(/0/g, "").length;
}

where binaryValue is the binary String eg: 1100