How to determine if a number is odd in JavaScript

Question

Can anyone point me to some code to determine if a number in JavaScript is even or odd

User · Answer

This can be solved with a small snippet of code  function isEven value        return   value   2     Hope this helps

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A simple function you can pass around  Uses the modulo operator     var is even   function x        return   x   2       is even 3  false is even 6  true

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Like many languages  Javascript has a modulus operator    that finds the remainder of division  If there is no remainder after division by 2  a number is even      this expression is true if  number  is even  false otherwise  number   2    0    This is a very common idiom for testing for even integers

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Using   will help you to do this     You can create couple of functions to do it for you    I prefer separte functions which are not attached to Number in Javascript like this which also checking if you passing number or not   odd function   var isOdd   function num      return  number    typeof num    NaN       num   2        even function   var isEven   function num      return isOdd num     NaN    isOdd num     isOdd num        and call it like this   isOdd 5      true isOdd 6      false isOdd 12      false isOdd 18      false isEven 18      true isEven  18        NaN  isEven  17        NaN  isOdd null       NaN  isEven  100       true

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lt script gt          function even odd                var num     document getElementById  number   value               if   num   2                   document getElementById  result   innerHTML    Entered Number is Odd                             else                  document getElementById  result   innerHTML    Entered Number is Even                                lt  script gt   lt  head gt   lt body gt       lt center gt           lt div id  error  gt  lt  div gt           lt center gt               lt h2 gt  Find Given Number is Even or Odd  lt  h2 gt               lt p gt Enter a value lt  p gt               lt input type  text  id  number    gt               lt button onclick  even odd     gt Check lt  button gt  lt br   gt               lt div id  result  gt  lt b gt  lt  b gt  lt  div gt           lt  center gt       lt  center gt   lt  body gt

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One liner in ES6 just because it s clean   const isEven    num    gt  num   2    0

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This is what I did    Array of numbers var numbers    1  2  3  4  5  6  7  8  9  10 32 23 643 67 5876 6345 34 3453     Array of even numbers var evenNumbers         Array of odd numbers var oddNumbers        function classifyNumbers arr       go through the numbers one by one   for var i 0  i lt  arr length-1  i          if  arr i    2    0              Push the number to the evenNumbers array         evenNumbers push arr i           else             Push the number to the oddNumbers array         oddNumbers push arr i                  classifyNumbers numbers    console log  Even numbers      evenNumbers   console log  Odd numbers      oddNumbers     For some reason I had to make sure the length of the array is less by one  When I don t do that  I get  undefined  in the last element of the oddNumbers array

User · Answer

Just executed this one in Adobe Dreamweaver  it works perfectly  i used if  isNaN mynmb    to check if the given Value is a number or not  and i also used  Math abs mynmb 2  to convert negative number to positive and calculate       lt  DOCTYPE html PUBLIC  -  W3C  DTD XHTML 1 0 Transitional  EN   http   www w3 org TR xhtml1 DTD xhtml1-transitional dtd  gt   lt html xmlns  http   www w3 org 1999 xhtml  gt   lt head gt    lt  head gt   lt body bgcolor     FFFFCC  gt       lt h3 align   center  gt  ODD OR EVEN  lt  h3 gt  lt table cellspacing    2  cellpadding    5  bgcolor  palegreen  gt           lt form name   formtwo gt               lt td align    center  gt                   lt center gt  lt BR   gt Enter a number                        lt input type text id  enter  name enter maxlength  10    gt                       lt input type button name   b3 value    Click Here  onClick   compute     gt                         lt b gt is lt b gt                    lt input type text id  outtxt  name output size  5  value    disabled   gt   lt  b gt  lt  b gt  lt  center gt  lt b gt  lt b gt                   lt BR   gt  lt BR   gt               lt  b gt  lt  b gt  lt  td gt  lt  form gt           lt  table gt        lt script type  text javascript  gt           function compute                       var enter   document getElementById  enter              var outtxt   document getElementById  outtxt               var mynmb   enter value            if  isNaN mynmb                             outtxt value    error                    alert   please enter a valid number                enter focus                return                        else                            if   mynmb 2    0     outtxt value    Even                    if   Math abs mynmb 2     1     outtxt value    Odd                                 lt  script gt   lt  body gt   lt  html gt

User · Answer

this works for arrays   function evenOrOdd numbers      const evenNumbers         const oddNumbers         numbers forEach number   gt        if  number   2     0          evenNumbers push number         else         oddNumbers push number                  console log  Even      evenNumbers     nOdd      oddNumbers      evenOrOdd  1  4  9  21  41  92      this should log out  4 92 1 9 21 41  for just a number   function evenOrOdd number      if  number   2     0        return  even          return  odd      console log evenOrOdd 4      this should output even to the console

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Many people misunderstand the meaning of odd   isOdd  str   should be false  Only an integer can be odd  isOdd 1 223  and isOdd -1 223  should be false  A float is not an integer  isOdd 0  should be false  Zero is an even integer  https   en wikipedia org wiki Parity of zero   isOdd -1  should be true  It s an odd integer    Solution  function isOdd n          Must be a number   if  isNaN n         return false            Number must not be a float   if   n   1      0        return false            Integer must not be equal to zero   if  n     0        return false            Integer must be odd   if   n   2      0        return true         return false      JS Fiddle  if needed   https   jsfiddle net 9dzdv593 8   1-liner  Javascript 1-liner solution  For those who don t care about readability   const isOdd   n   gt    isNaN n   amp  amp    n   1      0   amp  amp   n     0    amp  amp    n   2      0    true   false

User · Answer

I d implement this to return a boolean   function isOdd  n        return    n   2          or   n   2      0       It ll work on both unsigned and signed numbers  When the modulus return -1 or 1 it ll get translated to true   Non-modulus solution   var is finite   isFinite  var is nan   isNaN   function isOdd  discriminant        if  is nan discriminant   amp  amp   is finite discriminant             return false                Unsigned numbers     if  discriminant  gt   0            while  discriminant  gt   1  discriminant -  2          Signed numbers       else           if  discriminant     -1  return true          while  discriminant  lt   -1  discriminant    2             return   discriminant

User · Answer

You could do something like this   function isEven value       if  value 2    0          return true      else         return false

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You can use a for statement and a conditional to determine if a number or series of numbers is odd   for  var i 1  i lt  5  i     if  i 2     0        console log i      This will print every odd number between 1 and 5

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if  X   2     0     else       Replace X with your number  can come from a variable   The If statement runs when the number is even  the Else when it is odd   If you just want to know if any given number is odd   if  X   2     0       Again  replace X with a number or variable

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A more functional approach in modern javascript   const NUMBERS    nul one two three four five six seven ocho nueve  split       const negate   f  gt      args   gt   f    args  const isOdd    n  gt  NUMBERS n   10  indexOf  e    -1 const isEven   negate isOdd

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Do I have to make an array really large that has a lot of even numbers   No  Use modulus      It gives you the remainder of the two numbers you are dividing   Ex  2   2   0 because 2 2   1 with 0 remainder   Ex2  3   2   1 because 3 2   1 with 1 remainder   Ex3  -7   2   -1 because -7 2   -3 with -1 remainder    This means if you mod any number x by 2  you get either 0 or 1 or -1  0 would mean it s even  Anything else would mean it s odd

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By using ternary operator  you we can find the odd even numbers     x000D   x000D  var num   2  x000D  result    num   2    0     even     odd  x000D  console log result   x000D   x000D   x000D

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Use the below code    x000D   x000D  function isOdd num    return num   2   x000D  console log  1 is     isOdd 1    x000D  console log  2 is     isOdd 2    x000D  console log  3 is     isOdd 3    x000D  console log  4 is     isOdd 4    x000D   x000D   x000D    1 represents an odd number  while 0 represents an even number

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Use my extensions     Number prototype isEven function         return this   2   0      Number prototype isOdd function         return  this isEven        then   var a 5    a isEven        False   a isOdd        True  if you are not sure if it is a Number   test it by the following branching     if a isOdd       a isOdd        UPDATE     if you would not use variable      5  isOdd     Performance    It turns out that Procedural paradigm is better than OOP paradigm    By the way   i performed  profiling in this FIDDLE   However   OOP way is still prettiest

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Every odd number when divided by two leaves remainder as 1 and every even number when divided by zero leaves a zero as remainder  Hence we can use this code    function checker number        return number 2  0 even odd

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in ES6   const isOdd   num   gt  num   2    1

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function isEven x    return  x 2   0    function isOdd x    return  isEven x

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With bitwise  codegolfing   var isEven n  gt  n amp 1   odd   even

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Subtract 2 to it recursively until you reach either -1 or 0  only works for positive integers obviously

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Use the bitwise AND operator    x000D   x000D  function oddOrEven x    x000D    return   x  amp  1      odd     even   x000D    x000D   x000D  function checkNumber argNumber    x000D    document getElementById  result   innerHTML    Number     argNumber     is     oddOrEven argNumber   x000D    x000D    x000D  checkNumber 17   x000D   lt div id  result  style  font-size 150  text-shadow  1px 1px 2px  CE5937    gt  lt  div gt  x000D   x000D   x000D    If you don t want a string return value  but rather a boolean one  use this   var isOdd   function x    return x  amp  1     var isEven    function x    return    x  amp  1

User · Answer

When you need to test if some variable is odd  you should first test if it is integer  Also  notice that when you calculate remainder on negative number  the result will be negative  -3   2     -1     function isOdd value      return typeof value      number   amp  amp     value should be a number     isFinite value   amp  amp                    value should be finite     Math floor value      value  amp  amp        value should be integer     value   2     0                      value should not be even     If Number isInteger is available  you may also simplify this code to   function isOdd value      return Number isInteger value          value should be integer     value   2     0                      value should not be even     Note  here  we test value   2     0 instead of value   2     1 is because of -3   2     -1  If you don t want -1 pass this test  you may need to change this line   Here are some test cases   isOdd               false isOdd  string       false isOdd Infinity      false isOdd NaN           false isOdd 0             false isOdd 1 1           false isOdd  1            false isOdd 1             true isOdd -1            true

User · Answer

How about this         var num   3   instead get your value here     var aa     Even    Odd         alert aa num   2

[javascript] How to determine if a number is odd in JavaScript

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