Best way to alphanumeric check in JavaScript

Question

What is the best way to perform an alphanumeric check on an INPUT field in JSP  I have attached my current code function validateCode         var TCode   document getElementById  quot TCode quot   value       for  var i   0  i  lt  TCode length  i              var char1   TCode charAt i           var cc   char1 charCodeAt 0            if   cc  gt  47  amp  amp  cc  lt  58      cc  gt  64  amp  amp  cc  lt  91      cc  gt  96  amp  amp  cc  lt  123               else               alert  quot Input is not alphanumeric quot                return false                       return true

User · Answer

If you want a simplest one-liner solution, then go for the accepted answer that uses regex.

However, if you want a faster solution then here's a function you can have.

_x000D_

console.log(isAlphaNumeric('a')); // true
console.log(isAlphaNumericString('HelloWorld96')); // true
console.log(isAlphaNumericString('Hello World!')); // false

/**
 * Function to check if a character is alpha-numeric.
 *
 * @param {string} c
 * @return {boolean}
 */
function isAlphaNumeric(c) {
  const CHAR_CODE_A = 65;
  const CHAR_CODE_Z = 90;
  const CHAR_CODE_AS = 97;
  const CHAR_CODE_ZS = 122;
  const CHAR_CODE_0 = 48;
  const CHAR_CODE_9 = 57;

  let code = c.charCodeAt(0);

  if (
    (code >= CHAR_CODE_A && code <= CHAR_CODE_Z) ||
    (code >= CHAR_CODE_AS && code <= CHAR_CODE_ZS) ||
    (code >= CHAR_CODE_0 && code <= CHAR_CODE_9)
  ) {
    return true;
  }

  return false;
}

/**
 * Function to check if a string is fully alpha-numeric.
 *
 * @param {string} s
 * @returns {boolean}
 */
function isAlphaNumericString(s) {
  for (let i = 0; i < s.length; i++) {
    if (!isAlphaNumeric(s[i])) {
      return false;
    }
  }

  return true;
}

_x000D_

User · Answer

Here are some notes  The real alphanumeric string is like  quot 0a0a0a0b0c0d quot  and not like  quot 000000 quot  or  quot qwertyuio quot   All the answers I read here  returned true in both cases  This is not right  If I want to check if my  quot 00000 quot  string is alphanumeric  my intuition is unquestionably FALSE  Why  Simple  I cannot find any letter char  So  is a simple numeric string  0-9   On the other hand  if I wanted to check my  quot abcdefg quot  string  my intuition is still FALSE  I don t see numbers  so it s not alphanumeric  Just alpha  a-zA-Z   The Michael Martin-Smucker s answer has been illuminating  However he was aimed at achieving better performance instead of regex  This is true  using a low level way there s a better perfomance  But results it s the same  The strings  quot 0123456789 quot   only numeric    quot qwertyuiop quot   only alpha  and  quot 0a1b2c3d4f4g quot   alphanumeric  returns TRUE as alphanumeric  Same regex    a-z0-9    i way  The reason why the regex does not work is as simple as obvious  The syntax    indicates or  not and  So  if is it only numeric or if is it only letters  regex returns true  But  the Michael Martin-Smucker s answer was nevertheless illuminating  For me  It allowed me to think at  quot low level quot   to create a real function that unambiguously processes an alphanumeric string  I called it like PHP relative function ctype alnum  edit 2020-02-18  Where  however  this checks OR and not AND   Here s the code   function ctype alnum str      var code  i  len    var isNumeric   false  isAlpha   false     I assume that it is all non-alphanumeric    for  i   0  len   str length  i  lt  len  i          code   str charCodeAt i        switch  true          case code  gt  47  amp  amp  code  lt  58     check if 0-9         isNumeric   true          break         case  code  gt  64  amp  amp  code  lt  91      code  gt  96  amp  amp  code  lt  123      check if A-Z or a-z         isAlpha   true          break         default             not 0-9  not A-Z or a-z         return false     stop function with false result  no more checks              return isNumeric  amp  amp  isAlpha     return the loop results  if both are true  the string is certainly alphanumeric     And here is a demo   x000D   x000D  function ctype alnum str      var code  i  len      var isNumeric   false  isAlpha   false    I assume that it is all non-alphanumeric       loop1    for  i   0  len   str length  i  lt  len  i          code   str charCodeAt i                             switch  true               case code  gt  47  amp  amp  code  lt  58     check if 0-9                 isNumeric   true                  break              case  code  gt  64  amp  amp  code  lt  91      code  gt  96  amp  amp  code  lt  123     check if A-Z or a-z                 isAlpha   true                  break              default     not 0-9  not A-Z or a-z                 return false    stop function with false result  no more checks                                        return isNumeric  amp  amp  isAlpha    return the loop results  if both are true  the string is certainly alphanumeric         input   on  keyup   function     if    this  val   length     0       results   html      return false   var isAlphaNumeric   ctype alnum    this  val             results   html           isAlphaNumeric     Yes     No                        x000D   lt script src  https   cdnjs cloudflare com ajax libs jquery 3 3 1 jquery min js  gt  lt  script gt   lt input id  input  gt    lt div gt  is Alphanumeric    lt span id  results  gt  lt  span gt   lt  div gt  x000D   x000D   x000D   This is an implementation of Michael Martin-Smucker s method in JavaScript

User · Answer

In a tight loop  it s probably better to avoid regex and hardcode your characters   const CHARS   new Set  0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ    function isAlphanumeric char        return CHARS has char

User · Answer

Removed NOT operation in alpha-numeric validation  Moved variables to block level scope  Some comments here and there  Derived from the best Micheal  x000D   x000D  function isAlphaNumeric   str           Iterating character by character to get ASCII code for each character      for   let i   0  len   str length  code   0  i  lt  len    i             Collecting charCode from i index value in a string        code   str charCodeAt  i             Validating charCode falls into anyone category        if             code  gt  47  amp  amp  code  lt  58     numeric  0-9               code  gt  64  amp  amp  code  lt  91     upper alpha  A-Z               code  gt  96  amp  amp  code  lt  123      lower alpha  a-z                continue                 If nothing satisfies then returning false        return false           After validating all the characters and we returning success message     return true      console log isAlphaNumeric  oye     console log isAlphaNumeric  oye123     console log isAlphaNumeric  oye 123     x000D   x000D   x000D

User · Answer

Check it with a regex   Javascript regexen don t have POSIX character classes  so you have to write character ranges manually   if   input string match    0-9a-z         show error or something     Here   means beginning of string and   means end of string  and  0-9a-z   means one or more of character from 0 to 9 OR from a to z   More information on Javascript regexen here  https   developer mozilla org en JavaScript Guide Regular Expressions

User · Answer

You can use this regex    a-z0-9    i

User · Answer

I would create a String prototype method   String prototype isAlphaNumeric   function       var regExp      A-Za-z0-9        return  this match regExp         Then  the usage would be   var TCode   document getElementById  TCode   value  return TCode isAlphaNumeric

User · Answer

On keypress event call the following method     function AlphaNumCheck e            var charCode    e which    e which   e keyCode          if  charCode    8  return true           var keynum          var keychar          var charcheck     a-zA-Z0-9            if  window event     IE                       keynum   e keyCode                    else               if  e which     Netscape Firefox Opera                               keynum   e which                            else return true                     keychar   String fromCharCode keynum           return charcheck test keychar           Further  this article also helps to understand JavaScript alphanumeric validation

User · Answer

To check whether input string is alphanumeric  simply use   input string match     w         null

User · Answer

You don t need to do it one at a time  Just do a test for any that are not alpha-numeric  If one is found  the validation fails   function validateCode        var TCode   document getElementById  TCode   value      if     a-zA-Z0-9   test  TCode              alert  Input is not alphanumeric           return false            return true            If there s at least one match of a non alpha numeric  it will return false

User · Answer

The asker s original inclination to use str charCodeAt i  appears to be faster than the regular expression alternative  In my test on jsPerf the RegExp option performs 66  slower in Chrome 36  and slightly slower in Firefox 31    Here s a cleaned-up version of the original validation code that receives a string and returns true or false   function isAlphaNumeric str      var code  i  len     for  i   0  len   str length  i  lt  len  i          code   str charCodeAt i       if    code  gt  47  amp  amp  code  lt  58   amp  amp     numeric  0-9            code  gt  64  amp  amp  code  lt  91   amp  amp     upper alpha  A-Z            code  gt  96  amp  amp  code  lt  123        lower alpha  a-z        return false              return true       Of course  there may be other considerations  such as readability  A one-line regular expression is definitely prettier to look at  But if you re strictly concerned with speed  you may want to consider this alternative

[javascript] Best way to alphanumeric check in JavaScript

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