How to check the value given is a positive or negative integer

Question

Lets say i have the value 10 assigned to a variable   var values   10    and i want to run a specific function if the value is a positive  if values    integer          do something with positive    else          do something with negative values      How would this be achieved

User · Answer

I know it s been some time  but there is a more elegant solution  From the mozilla   docs   Math sign parseInt -3     It will give you -1 for negative  0 for zero and 1 for positive

User · Answer

if values  gt   0        as zero is more likely positive than negative   else

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if  values  gt  0           Do Something

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To check a number is positive  negative or negative zero  Check its sign using  Math sign   method it will provide you -1 -0 0 and 1 on the basis of positive negative and negative zero or zero numbers    Math sign -3     -1  Math sign 3     1  Math sign -0     -0  Math sign 0     0

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1 Checking for positive value  In javascript simple comparison like  value     0 does not provide us with answer due to existence of -0 and  0  This is concept has it roots in derivative equations  Bellow example of those values and its properties   var negativeZero   -0  var negativeZero   -1   Number POSITIVE INFINITY  var negativeZero   -Number MIN VALUE   Number POSITIVE INFINITY   var positiveZero   0  var positiveZero   1   Number POSITIVE INFINITY  var positiveZero   Number MIN VALUE   Number POSITIVE INFINITY   -0      0                        true 1   -0                           -Infinity  0   -0                          NaN -0   Number POSITIVE INFINITY    NaN   Having that in mind we can write function like bellow to check for sign of given number   function isPositive  number        if   number  gt  0              return true            if  number  lt  0            return false            if   1   number     Number POSITIVE INFINITY             return true            return false      2a Checking for number being an Integer  in mathematical sense   To check that number is an integer we can use bellow function   function isInteger  number        return parseInt number      number        in ECMA Script 6 use Number isInteger   2b Checking for number being an Integer  in computer science   In this case we are checking that number does not have any exponential part  please note that in JS numbers are represented in double-precision floating-point format  However in javascript it is more usable to check that value is  safe integer   http   people mozilla org  jorendorff es6-draft html sec-number max safe integer  - to put it simple it means that we can add substract 1 to  safe integer  and be sure that result will be same as expected from math lessons  To illustrate what I mean  result of some unsafe operations bellow   Number MAX SAFE INTEGER   1     Number MAX SAFE INTEGER   2              true Number MAX SAFE INTEGER   2   1     Number MAX SAFE INTEGER   2   4      true   Ok  so to check that number is safe integer we can use Number MAX SAFE INTEGER   Number MIN SAFE INTEGER and parseInt to ensure that number is integer at all   function isSafeInteger  number        return parseInt number      number      amp  amp  number  lt    Number MAX SAFE INTEGER      amp  amp  number  gt    Number MIN SAFE INTEGER       in ECMA Script 6 use Number isSafeInteger

User · Answer

I thought here you wanted to do the action if it is positive   Then would suggest   if  Math sign number to test      1         function to run when positive

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You should first check if the input value is interger with isNumeric   function  Then add the condition or greater than 0   This is the jQuery code for it   function isPositiveInteger n            return    isNumeric n   amp  amp   n  gt  0

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Am I the only one who read this and realized that none of the answers addressed the  integer  part of the question   The problem  var myInteger   6  var myFloat   6 2  if  myInteger  gt  0          Cool  we correctly identified this as a positive integer if  myFloat  gt  0          Oh  no  That s not an integer    The solution  To guarantee that you re dealing with an integer  you want to cast your value to an integer then compare it with itself   if  parseInt  myInteger      myInteger  amp  amp  myInteger  gt  0          myInteger is an integer AND it s positive if  parseInt  myFloat      myFloat  amp  amp  myFloat  gt  0          myFloat is NOT an integer  so parseInt myFloat     myFloat   Some neat optimizations  As a bonus  there are some shortcuts for converting from a float to an integer in JavaScript  In JavaScript  all bitwise operators         amp   etc  will cast your number to an integer before operating  I assume this is because 99  of developers don t know the IEEE floating point standard and would get horribly confused when  200   2  evaluated to 400 ish   These shortcuts tend to run faster than Math floor or parseInt  and they take up fewer bytes if you re trying to eke out the smallest possible code   if  myInteger   0    myInteger  amp  amp  myInteger  gt  0          Woot  if  myFloat   0    myFloat  amp  amp  myFloat  gt  0          Woot  again    But wait  there s more   These bitwise operators are working on 32-bit signed integers  This means the highest bit is the sign bit  By forcing the sign bit to zero your number will remain unchanged only if it was positive  You can use this to check for positiveness AND integerness in a single blow      Where 2147483647   01111111111111111111111111111111 in binary if   myInteger  amp  2147483647     myInteger          myInteger is BOTH positive and an integer if   myFloat  amp  2147483647     myFloat          Won t happen   note bit AND operation is wrapped with parenthesis to make it work in chrome  console    If you have trouble remembering this convoluted number  you can also calculate it before-hand as such   var specialNumber     1  lt  lt  31     Checking for negatives  Per  Reinsbrain s comment  a similar bitwise hack can be used to check for a negative integer  In a negative number  we do want the left-most bit to be a 1  so by forcing this bit to 1 the number will only remain unchanged if it was negative to begin with      Where -2147483648   10000000000000000000000000000000 in binary if   myInteger   -2147483648     myInteger          myInteger is BOTH negative and an integer if   myFloat   -2147483648     myFloat          Won t happen   This special number is even easier to calculate   var specialNumber   1  lt  lt  31    Edge cases  As mentioned earlier  since JavaScript bitwise operators convert to 32-bit integers  numbers which don t fit in 32 bits  greater than  2 billion  will fail  You can fall back to the longer solution for these   if  parseInt 123456789000     123456789000  amp  amp  123456789000  gt  0     However even this solution fails at some point  because parseInt is limited in its accuracy for large numbers  Try the following and see what happens   parseInt 123123123123123123123      That s 7  123 s   On my computer  in Chrome console  this outputs  123123123123123130000  The reason for this is that parseInt treats the input like a 64-bit IEEE float  This provides only 52 bits for the mantissa  meaning a maximum value of  4 5e15 before it starts rounding

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For checking positive integer   var isPositiveInteger   function n            return    isNumeric n    amp  amp   Math floor n     n   amp  amp   n  gt  0

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You can use shifting bit operator  but it want get the difference between -0 and  0 like Math sign x  does   let num   -45  if num  gt  gt  31     -1      alert  Negative number    else     alert  Positive number      https   jsfiddle net obxptgze

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Positive integer   if  parseInt values  10   gt  0

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if   values  gt  0            Yeah  it s positive

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To just check  this is the fastest way  it seems   var sign   number  gt  0   1   number    0   0   -1     Is  number   greater than zero  Yes  Return 1 to  sign     Otherwise  does  number  equal zero   Yes   Return 0 to  sign       Otherwise  return -1 to  sign     It tells you if the sign is positive  returns 1   or equal to zero  returns 0   and otherwise  returns -1    This is a good solution because 0 is not positive  and it is not negative  but it may be your var     Failed attempt   var sign   number  gt  0   1   -1       will count 0 as a negative integer  which is wrong   If you re trying to set up conditionals  you can adjust accordingly   Here s are two analogous example of an if else-if statement   Example 1   number   prompt  Pick a number     if  number  gt  0     alert  Oh baby  your number is so big      else if  number    0     alert  Hey  there s nothing there      else    alert  Wow  that thing s so small it might be negative        Example 2       number   prompt  Pick a number      var sign   number  gt  0   1   number    0   0   -1   if  sign    1     alert  Oh baby  your number is so big           number    else if  sign    0     alert  Hey  there s nothing there           number    else if  sign    -1     alert  Wow  that thing s so small it might be negative           number

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if   values  gt  0           you got a positive value  else        you got a negative or zero value

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simply write   if values  gt  0     positive   else    negative

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I use in this case and it works     var pos   0   var sign   0  var zero   0  var neg   0  for  var i in arr         sign   arr i   gt  0   1   arr i     0   0   -1      if  sign     0            zero           else if  sign     1             pos          else           neg

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Starting from the base that the received value is a number and not a string  what about use Math abs    This JavaScript native function returns the absolute value of a number   Math abs -1     1   So you can use it this way   var a   -1  if a    Math abs a           false     var b   1     if b    Math abs b           true

[javascript] How to check the value given is a positive or negative integer?

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