[javascript] How do I convert an integer to binary in JavaScript?

I’d like to see integers, positive or negative, in binary.

Rather like this question, but for JavaScript.

Try

num.toString(2);

The 2 is the radix and can be any base between 2 and 36

source here

UPDATE:

This will only work for positive numbers, Javascript represents negative binary integers in two's-complement notation. I made this little function which should do the trick, I haven't tested it out properly:

function dec2Bin(dec)
{
    if(dec >= 0) {
        return dec.toString(2);
    }
    else {
        /* Here you could represent the number in 2s compliment but this is not what 
           JS uses as its not sure how many bits are in your number range. There are 
           some suggestions https://stackoverflow.com/questions/10936600/javascript-decimal-to-binary-64-bit 
        */
        return (~dec).toString(2);
    }
}

I had some help from here

A simple way is just...

Number(42).toString(2);

// "101010"

I used a different approach to come up with something that does this. I've decided to not use this code in my project, but I thought I'd leave it somewhere relevant in case it is useful for someone.

• Doesn't use bit-shifting or two's complement coercion.
• You choose the number of bits that comes out (it checks for valid values of '8', '16', '32', but I suppose you could change that)
• You choose whether to treat it as a signed or unsigned integer.
• It will check for range issues given the combination of signed/unsigned and number of bits, though you'll want to improve the error handling.
• It also has the "reverse" version of the function which converts the bits back to the int. You'll need that since there's probably nothing else that will interpret this output :D

function intToBitString(input, size, unsigned) {_x000D_
 if ([8, 16, 32].indexOf(size) == -1) {_x000D_
  throw "invalid params";_x000D_
 }_x000D_
 var min = unsigned ? 0 : - (2 ** size / 2);_x000D_
        var limit = unsigned ? 2 ** size : 2 ** size / 2;_x000D_
 if (!Number.isInteger(input) || input < min || input >= limit) {_x000D_
  throw "out of range or not an int";_x000D_
 }_x000D_
 if (!unsigned) {_x000D_
  input += limit;_x000D_
 }_x000D_
 var binary = input.toString(2).replace(/^-/, '');_x000D_
 return binary.padStart(size, '0');_x000D_
}_x000D_
_x000D_
function bitStringToInt(input, size, unsigned) {_x000D_
 if ([8, 16, 32].indexOf(size) == -1) {_x000D_
  throw "invalid params";_x000D_
 }_x000D_
 input = parseInt(input, 2);_x000D_
 if (!unsigned) {_x000D_
  input -= 2 ** size / 2;_x000D_
 }_x000D_
 return input;_x000D_
}_x000D_
_x000D_
_x000D_
// EXAMPLES_x000D_
_x000D_
var res;_x000D_
console.log("(uint8)10");_x000D_
res = intToBitString(10, 8, true);_x000D_
console.log("intToBitString(res, 8, true)");_x000D_
console.log(res);_x000D_
console.log("reverse:", bitStringToInt(res, 8, true));_x000D_
console.log("---");_x000D_
_x000D_
console.log("(uint8)127");_x000D_
res = intToBitString(127, 8, true);_x000D_
console.log("intToBitString(res, 8, true)");_x000D_
console.log(res);_x000D_
console.log("reverse:", bitStringToInt(res, 8, true));_x000D_
console.log("---");_x000D_
_x000D_
console.log("(int8)127");_x000D_
res = intToBitString(127, 8, false);_x000D_
console.log("intToBitString(res, 8, false)");_x000D_
console.log(res);_x000D_
console.log("reverse:", bitStringToInt(res, 8, false));_x000D_
console.log("---");_x000D_
_x000D_
console.log("(int8)-128");_x000D_
res = intToBitString(-128, 8, false);_x000D_
console.log("intToBitString(res, 8, true)");_x000D_
console.log(res);_x000D_
console.log("reverse:", bitStringToInt(res, 8, true));_x000D_
console.log("---");_x000D_
_x000D_
console.log("(uint16)5000");_x000D_
res = intToBitString(5000, 16, true);_x000D_
console.log("intToBitString(res, 16, true)");_x000D_
console.log(res);_x000D_
console.log("reverse:", bitStringToInt(res, 16, true));_x000D_
console.log("---");_x000D_
_x000D_
console.log("(uint32)5000");_x000D_
res = intToBitString(5000, 32, true);_x000D_
console.log("intToBitString(res, 32, true)");_x000D_
console.log(res);_x000D_
console.log("reverse:", bitStringToInt(res, 32, true));_x000D_
console.log("---");

function dec2bin(dec){
    return (dec >>> 0).toString(2);
}

dec2bin(1);    // 1
dec2bin(-1);   // 11111111111111111111111111111111
dec2bin(256);  // 100000000
dec2bin(-256); // 11111111111111111111111100000000

You can use Number.toString(2) function, but it has some problems when representing negative numbers. For example, (-1).toString(2) output is "-1".

To fix this issue, you can use the unsigned right shift bitwise operator (>>>) to coerce your number to an unsigned integer.

If you run (-1 >>> 0).toString(2) you will shift your number 0 bits to the right, which doesn't change the number itself but it will be represented as an unsigned integer. The code above will output "11111111111111111111111111111111" correctly.

This question has further explanation.

-3 >>> 0 (right logical shift) coerces its arguments to unsigned integers, which is why you get the 32-bit two's complement representation of -3.

This answer attempts to address inputs with an absolute value in the range of 2147483648₁₀ (2³¹) – 9007199254740991₁₀ (2⁵³-1).

In JavaScript, numbers are stored in 64-bit floating point representation, but bitwise operations coerce them to 32-bit integers in two's complement format, so any approach which uses bitwise operations restricts the range of output to -2147483648₁₀ (-2³¹) – 2147483647₁₀ (2³¹-1).

However, if bitwise operations are avoided and the 64-bit floating point representation is preserved by using only mathematical operations, we can reliably convert any safe integer to 64-bit two's complement binary notation by sign-extending the 53-bit twosComplement:

function toBinary (value) {
  if (!Number.isSafeInteger(value)) {
    throw new TypeError('value must be a safe integer');
  }

  const negative = value < 0;
  const twosComplement = negative ? Number.MAX_SAFE_INTEGER + value + 1 : value;
  const signExtend = negative ? '1' : '0';

  return twosComplement.toString(2).padStart(53, '0').padStart(64, signExtend);
}

function format (value) {
  console.log(value.toString().padStart(64));
  console.log(value.toString(2).padStart(64));
  console.log(toBinary(value));
}

format(8);
format(-8);
format(2**33-1);
format(-(2**33-1));
format(2**53-1);
format(-(2**53-1));
format(2**52);
format(-(2**52));
format(2**52+1);
format(-(2**52+1));

.as-console-wrapper{max-height:100%!important}

For older browsers, polyfills exist for the following functions and values:

• Number.isSafeInteger()
• Number.isInteger()
• Number.MAX_SAFE_INTEGER
• String.prototype.padStart()

As an added bonus, you can support any radix (2–36) if you perform the two's complement conversion for negative numbers in ?64 / log₂(radix)? digits by using BigInt:

function toRadix (value, radix) {
  if (!Number.isSafeInteger(value)) {
    throw new TypeError('value must be a safe integer');
  }

  const digits = Math.ceil(64 / Math.log2(radix));
  const twosComplement = value < 0
    ? BigInt(radix) ** BigInt(digits) + BigInt(value)
    : value;

  return twosComplement.toString(radix).padStart(digits, '0');
}

console.log(toRadix(0xcba9876543210, 2));
console.log(toRadix(-0xcba9876543210, 2));
console.log(toRadix(0xcba9876543210, 16));
console.log(toRadix(-0xcba9876543210, 16));
console.log(toRadix(0x1032547698bac, 2));
console.log(toRadix(-0x1032547698bac, 2));
console.log(toRadix(0x1032547698bac, 16));
console.log(toRadix(-0x1032547698bac, 16));

.as-console-wrapper{max-height:100%!important}

If you are interested in my old answer that used an ArrayBuffer to create a union between a Float64Array and a Uint16Array, please refer to this answer's revision history.

This is my code:

var x = prompt("enter number", "7");
var i = 0;
var binaryvar = " ";

function add(n) {
    if (n == 0) {
        binaryvar = "0" + binaryvar; 
    }
    else {
        binaryvar = "1" + binaryvar;
    }
}

function binary() {
    while (i < 1) {
        if (x == 1) {
            add(1);
            document.write(binaryvar);
            break;
        }
        else {
            if (x % 2 == 0) {
                x = x / 2;
                add(0);
            }
            else {
                x = (x - 1) / 2;
                add(1);
            }
        }
    }
}

binary();

The binary in 'convert to binary' can refer to three main things. The positional number system, the binary representation in memory or 32bit bitstrings. (for 64bit bitstrings see Patrick Roberts' answer)

1. Number System

(123456).toString(2) will convert numbers to the base 2 positional numeral system. In this system negative numbers are written with minus signs just like in decimal.

2. Internal Representation

The internal representation of numbers is 64 bit floating point and some limitations are discussed in this answer. There is no easy way to create a bit-string representation of this in javascript nor access specific bits.

3. Masks & Bitwise Operators

MDN has a good overview of how bitwise operators work. Importantly:

Bitwise operators treat their operands as a sequence of 32 bits (zeros and ones)

Before operations are applied the 64 bit floating points numbers are cast to 32 bit signed integers. After they are converted back.

Here is the MDN example code for converting numbers into 32-bit strings.

function createBinaryString (nMask) {
  // nMask must be between -2147483648 and 2147483647
  for (var nFlag = 0, nShifted = nMask, sMask = ""; nFlag < 32;
       nFlag++, sMask += String(nShifted >>> 31), nShifted <<= 1);
  return sMask;
}

createBinaryString(0) //-> "00000000000000000000000000000000"
createBinaryString(123) //-> "00000000000000000000000001111011"
createBinaryString(-1) //-> "11111111111111111111111111111111"
createBinaryString(-1123456) //-> "11111111111011101101101110000000"
createBinaryString(0x7fffffff) //-> "01111111111111111111111111111111"

This is the solution . Its quite simple as a matter of fact

function binaries(num1){ 
        var str = num1.toString(2)
        return(console.log('The binary form of ' + num1 + ' is: ' + str))
     }
     binaries(3

)

        /*
         According to MDN, Number.prototype.toString() overrides 
         Object.prototype.toString() with the useful distinction that you can 
         pass in a single integer argument. This argument is an optional radix, 
         numbers 2 to 36 allowed.So in the example above, we’re passing in 2 to 
         get a string representation of the binary for the base 10 number 100, 
         i.e. 1100100.
        */

This is how I manage to handle it:

const decbin = nbr => {
  if(nbr < 0){
     nbr = 0xFFFFFFFF + nbr + 1
  }
  return parseInt(nbr, 10).toString(2)
};

got it from this link: https://locutus.io/php/math/decbin/

One more alternative

const decToBin = dec => {
  let bin = '';
  let f = false;

  while (!f) {
    bin = bin + (dec % 2);    
    dec = Math.trunc(dec / 2);  

    if (dec === 0 ) f = true;
  }

  return bin.split("").reverse().join("");
}

console.log(decToBin(0));
console.log(decToBin(1));
console.log(decToBin(2));
console.log(decToBin(3));
console.log(decToBin(4));
console.log(decToBin(5));
console.log(decToBin(6));

we can also calculate the binary for positive or negative numbers as below:

function toBinary(n){
    let binary = "";
    if (n < 0) {
      n = n >>> 0;
    }
    while(Math.ceil(n/2) > 0){
        binary = n%2 + binary;
        n = Math.floor(n/2);
    }
    return binary;
}

console.log(toBinary(7));
console.log(toBinary(-7));

You can write your own function that returns an array of bits. Example how to convert number to bits

Divisor| Dividend| bits/remainder

2 | 9 | 1

2 | 4 | 0

2 | 2 | 0

~ | 1 |~

example of above line: 2 * 4 = 8 and remainder is 1 so 9 = 1 0 0 1

function numToBit(num){
    var number = num
    var result = []
    while(number >= 1 ){
        result.unshift(Math.floor(number%2))
        number = number/2
    }
    return result
}

Read remainders from bottom to top. Digit 1 in the middle to top.