Converting large numbers from binary to decimal and back in JavaScript

Question

I have a very large number represented as binary in JavaScript:

 var largeNumber = \'110100110101101000010100111110100101110111110000100101110001111100111110         


        

Answer 1

If you're looking to transfer a large amount of binary data, you should use BigInt. BigInt allows you to represent an arbitrary number of bits.

// parse large number from string
let numString = '1101001101011010000101001111101001011101111100001001'

// as number
let num = BigInt('0b' + numString)

// now num holds large number equivalent to numString
console.log(num)  // 3718141639515913n

// print as base 2
console.log(num.toString(2))  // 1101001101011010000101001111101001011101111100001001

Helper functions

// some helper functions

// get kth bit from right
function getKthBit(x, k){
  return (x & (1n << k)) >> k;
}

// set kth bit from right to 1
function setKthBit(x, k){
  return (1n << k) | x;
}

// set kth bit from right to 0
function unsetKthBit(x, k){
  return (x & ~(1n << k));
}

getKthBit(num, 0n);  
// 1n

getKthBit(num, 5n);  
// 0n

setKthBit(num, 1n).toString(2); 
// 1101001101011010000101001111101001011101111100001011

setKthBit(num, 4n); 
// 1101001101011010000101001111101001011101111100011001

unsetKthBit(num, 0n).toString(2);
// 1101001101011010000101001111101001011101111100001000

unsetKthBit(num, 0n).toString(2);
// 1101001101011010000101001111101001011101111100000001

For convenience you may want to add this to BigInt if you're going to be serializing back to the client. Then you can read it back as a string. Otherwise you will get "Uncaught TypeError: Do not know how to serialize a BigInt" because for some reason Javascript Object Notation doesn't know how to serialize one of the types in Javascript.

    Object.defineProperty(BigInt.prototype, "toJSON", {
        get() {
            "use strict";
            return () => this.toString() + 'n';
        }
    });