How do I convert an integer to binary in JavaScript

Question

I   d like to see integers  positive or negative  in binary   Rather like this question  but for JavaScript

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This is how I manage to handle it  const decbin   nbr   gt      if nbr  lt  0        nbr   0xFFFFFFFF   nbr   1       return parseInt nbr  10  toString 2      got it from this link  https   locutus io php math decbin

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A simple way is just     Number 42  toString 2        101010

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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  lt  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

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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  amp  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  lt  32         nFlag    sMask    String nShifted  gt  gt  gt  31   nShifted  lt  lt   1     return sMask     createBinaryString 0    - gt   00000000000000000000000000000000  createBinaryString 123    - gt   00000000000000000000000001111011  createBinaryString -1    - gt   11111111111111111111111111111111  createBinaryString -1123456    - gt   11111111111011101101101110000000  createBinaryString 0x7fffffff    - gt   01111111111111111111111111111111

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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

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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    x000D   x000D  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  lt  min    input  gt   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  ---    x000D   x000D   x000D

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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   x000D   x000D  function toBinary  value      if   Number isSafeInteger value         throw new TypeError  value must be a safe integer           const negative   value  lt  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    x000D   as-console-wrapper max-height 100  important  x000D   x000D   x000D   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   x000D   x000D  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  lt  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    x000D   as-console-wrapper max-height 100  important  x000D   x000D   x000D   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

User · Answer

we can also calculate the binary for positive or negative numbers as below   x000D   x000D  function toBinary n       let binary           if  n  lt  0          n   n  gt  gt  gt  0            while Math ceil n 2   gt  0           binary   n 2   binary          n   Math floor n 2             return binary     console log toBinary 7    console log toBinary -7    x000D   x000D   x000D

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One more alternative  const decToBin   dec   gt      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

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function dec2bin dec       return  dec  gt  gt  gt  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   gt  gt  gt   to coerce your number to an unsigned integer   If you run  -1  gt  gt  gt  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  gt  gt  gt  0  right logical shift  coerces its arguments to unsigned integers  which is why you get the 32-bit two s complement representation of -3

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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  gt   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

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A solution i d go with that s fine for 32-bits  is the code the end of this answer  which is from developer mozilla org MDN   but with some lines added for A formatting and B checking that the number is in range   Some suggested x toString 2  which doesn t work for negatives  it just sticks a minus sign in there for them  which is no good   Fernando mentioned a simple solution of  x gt  gt  gt 0  toString 2   which is fine for negatives  but has a slight issue when x is positive  It has the output starting with 1  which for positive numbers isn t proper 2s complement    Anybody that doesn t understand the fact of positive numbers starting with 0 and negative numbers with 1  in 2s complement  could check this SO QnA on 2s complement  What is    2  39 s Complement        A solution could involve prepending a 0 for positive numbers  which I did in an earlier revision of this answer  And one could accept sometimes having a 33bit number  or one could make sure that the number to convert is within range   - 2 31  lt  x lt 2 31-1  So the number is always 32bits   But rather than do that  you can go with this solution on mozilla org  Patrick s answer and code is long and apparently works for 64-bit  but had a bug that a commenter found  and the commenter fixed patrick s bug  but patrick has some  magic number  in his code that he didn t comment about and has forgotten about and patrick no longer fully understands his own code   why it works   Annan had some incorrect and unclear terminology but mentioned a solution by developer mozilla org https   developer mozilla org en-US docs Web JavaScript Reference Operators Bitwise Operators  This works for 32-bit numbers    The code is pretty compact  a function of three lines   But I have added a regex to format the output in groups of 8 bits  Based on How to print a number with commas as thousands separators in JavaScript   I just amended it from grouping it in 3s right to left and adding commas  to grouping in 8s right to left  and adding spaces   And  while mozilla made a comment about the size of nMask the number fed in   that it has to be in range   they didn t test for or throw an error when the number is out of range  so i ve added that    I m not sure why they named their parameter  nMask  but i ll leave that as is   Reference  https   developer mozilla org en-US docs Web JavaScript Reference Operators Bitwise Operators     x000D   x000D  function createBinaryString nMask    x000D       nMask must be between -2147483648 and 2147483647 x000D    if  nMask  gt  2  31-1   x000D       throw  number too large  number shouldn t be  gt  2  31-1     added x000D    if  nMask  lt  -1  2  31   x000D       throw  number too far negative  number shouldn t be  lt  2  31    added x000D    for  var nFlag   0  nShifted   nMask  sMask       nFlag  lt  32  x000D         nFlag    sMask    String nShifted  gt  gt  gt  31   nShifted  lt  lt   1   x000D    sMask sMask replace   B      8          g          added x000D    return sMask  x000D    x000D   x000D   x000D  console log createBinaryString -1          11111111 11111111 11111111 11111111  x000D  console log createBinaryString 1024        00000000 00000000 00000100 00000000  x000D  console log createBinaryString -2          11111111 11111111 11111111 11111110  x000D  console log createBinaryString -1024       11111111 11111111 11111100 00000000  x000D   x000D   x000D

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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  gt   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

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

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