How can I check for an empty undefined null string in JavaScript

Question

I saw this question  but I didn t see a JavaScript specific example  Is there a simple string Empty available in JavaScript  or is it just a case of checking for

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var x        var patt      s   g  isBlank   patt test x   alert isBlank      Is it blank or not   x   x replace   s  g          Another way of replacing blanks with    if  x            alert  ya it is blank

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All the previous answers are good  but this will be even better  Use dual NOT operators       if    str           Some code here    Or use type casting  if  Boolean str            Code here    Both do the same function  Typecast the variable to Boolean  where str is a variable  It returns false for null  undefined  0  000   quot  quot   false  It returns true for string  quot 0 quot  and whitespace  quot   quot

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You can able to validate following ways and understand the difference    x000D   x000D  var j   undefined  x000D  console log  typeof j     undefined      true   false    x000D  var j   null   x000D  console log  j    null     true   false    x000D  var j       x000D  console log   j     true   false    x000D  var j    Hi   x000D  console log   j     true   false    x000D   x000D   x000D

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Check all the below scenarios    null undefined 0     the empty string  false NaN

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The closest thing you can get to str Empty  with the precondition that str is a String  is   if   str length

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Try   if  str  amp  amp  str trim   length

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To check if it is empty   var str    Hello World    var n   str length  if n         alert  THE STRING str is EMPTY       To check if it isn t empty  var str    Hello World    var n   str length  if n        alert  THE STRING str isn t EMPTY

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I did some research on what happens if you pass a non-string and non-empty null value to a tester function  As many know   0        is true in JavaScript  but since 0 is a value and not empty or null  you may want to test for it   The following two functions return true only for undefined  null  empty whitespace values and false for everything else  such as numbers  Boolean  objects  expressions  etc   function IsNullOrEmpty value        return  value    null    value            function IsNullOrWhiteSpace value        return  value    null       S  test value        More complicated examples exists  but these are simple and give consistent results  There is no need to test for undefined  since it s included in  value    null  check  You may also mimic C  behaviour by adding them to String like this   String IsNullOrEmpty   function  value            You do not want to put it in Strings prototype  because if the instance of the String-class is null  it will error   String prototype IsNullOrEmpty   function  value          var myvar   null  if  1    2    myvar    OK        Could be set myvar IsNullOrEmpty       Throws error   I tested with the following value array  You can loop it through to test your functions if in doubt      Helper items var MyClass   function  b    this a    Hello World    this b   b     MyClass prototype hello   function      if  this b    null    alert this a     else   alert this b        var z  var arr        0  Explanation for printing  1  actual value       undefined   undefined          var  z   z         null   null         empty              space               tab     t          newline     n          carriage return     r             r  n      r n             n  r      n r              t   n        t  n             txt   t test   n      txt  t test  n           txt     txt           undefined     undefined           null     null           0     0           1     1           1 5     1 5           1 5     1 5       Valid number in some locales  not in JavaScript       comma               dot                 5      5          0   0         0 0   0 0         1   1         1 5   1 5         NaN   NaN           S      S          true   true         false   false         function  returns true   function      return true             function  returns false   function      return false             function  returns null   function      return null             function  returns string   function      return  test              function  returns undefined   function                 MyClass   MyClass         new MyClass   new MyClass           empty object              non-empty object     a   a   match   bogus   test   bogus           object with toString  string     a   a   match   bogus   test   bogus   toString  function      return  test               object with toString  null     a   a   match   bogus   test   bogus   toString  function      return null

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To check if it is exactly an empty string   if val            To check if it is an empty string OR a logical equivalent for no-value  null  undefined  0  NaN  false         if  val

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This function has worked well for me  assuring that it s both a string and not empty  isNonBlankString   function s    return   typeof s      string     s instanceof String   amp  amp  s

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If one needs to detect not only empty but also blank strings  I ll add to Goral s answer   function isEmpty s       return  s length         function isBlank s       return isEmpty s trim

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Very generic  quot All-In-One quot  Function  not recommended though   function is empty x        return                                                               don t put newline after return          typeof x     undefined                             x    null                            x    false           same as   x                           x length    0                            x    0                note this line  you might not need this                             x     quot  quot                             x replace   s g  quot  quot       quot  quot                                  s   test x                                s    test x             However  I don t recommend to use that  because your target variable should be of specific type  i e  string  or numeric  or object    so apply the checks that are relative to that variable

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I usually use something like this   if   str length           Do something

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You should always check for the type too  since JavaScript is a duck typed language  so you may not know when and how the data changed in the middle of the process  So  here s the better solution   x000D   x000D      let undefinedStr      if   undefinedStr          console log  String is undefined                   let emptyStr           if   emptyStr          console log  String is empty                   let nullStr   null      if   nullStr          console log  String is null          x000D   x000D   x000D

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You could also go with regular expressions   if     s     test str         Checks for strings that are either empty or filled with whitespace

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I would not worry too much about the most efficient method  Use what is most clear to your intention  For me that s usually strVar         As per the comment from Constantin  if strVar could some how end up containing an integer 0 value  then that would indeed be one of those intention-clarifying situations

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For checking if a string is empty  null or undefined I use   function isEmpty str        return   str    0     str length       For checking if a string is blank  null or undefined I use   function isBlank str        return   str       s    test str        For checking if a string is blank or contains only white-space   String prototype isEmpty   function         return  this length     0     this trim

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Also  in case you consider a whitespace filled string as  empty    You can test it with this regular expression      S  test string      Returns true if blank

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Lots of useful information here  but in my opinion  one of the most important elements was not addressed  null  undefined  and  quot  quot  are all falsy  When evaluating for an empty string  it s often because you need to replace it with something else  In which case  you can expect the following behavior  var a    quot  quot  var b   null var c   undefined  console log a     quot falsy string provided quot      prints - gt  quot falsy string provided quot  console log b     quot falsy string provided quot      prints - gt  quot falsy string provided quot  console log c     quot falsy string provided quot      prints - gt  quot falsy string provided quot   With that in mind  a method or function that can return whether or not a string is  quot  quot   null  or undefined  an invalid string  versus a valid string is as simple as this  const validStr    str    gt  str   true   false  validStr undefined     returns false validStr null     returns false validStr  quot  quot      returns false validStr  quot My String quot      returns true  I hope that s helpful

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Meanwhile we can have one function that checks for all  empties  like null  undefined                   So I just wrote this   var isEmpty   function data        if typeof data       object            if JSON stringify data              JSON stringify data                         return true           else if  data               return true                    return false       else if typeof data       string            if  data trim                 return true                    return false       else if typeof data       undefined            return true       else          return false            Use cases and results   console log isEmpty        true console log isEmpty null       true console log isEmpty          true console log isEmpty            true console log isEmpty undefined       true console log isEmpty          true console log isEmpty          true console log isEmpty 0       false console log isEmpty  Hey        false

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function tell         var pass   document getElementById  pasword   value      var plen   pass length          Now you can check if your string is empty as like     if plen  0                alert  empty              else               alert  you entered something              lt input type  text  id  pasword    gt    This is also a generic way to check if field is empty

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You can use lodash    isEmpty value    It covers a lot of cases like         null  undefined  etc   But it always returns true for Number type of JavaScript primitive data types like   isEmpty 10  or   isEmpty Number MAX VALUE  both returns true

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I didn t see a good answer here  at least not an answer that fits for me   So I decided to answer myself   value     undefined    value     null    value          You need to start checking if it s undefined  Otherwise your method can explode  and then you can check if it equals null or is equal to an empty string   You cannot have    or only if value  since if you check 0 it s going to give you a false answer  0 is false    With that said  wrap it up in a method like   public static isEmpty value  any   boolean       return value     undefined    value     null    value            PS   You don t need to check typeof  since it would explode and throw even before it enters the method

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If you need to make sure that the string is not just a bunch of empty spaces  I m assuming this is for form validation  you need to do a replace on the spaces   if str replace   s g

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The Underscore js JavaScript library  http   underscorejs org   provides a very useful   isEmpty   function for checking for empty strings and other empty objects   Reference  http   underscorejs org  isEmpty     isEmpty    isEmpty object     Returns true if an enumerable object contains no values  no enumerable own-properties   For strings and array-like objects   isEmpty checks if the length property is 0         isEmpty  1  2  3           false        isEmpty            true   Other very useful Underscore js functions include    http   underscorejs org  isNull    isNull object  http   underscorejs org  isUndefined   isUndefined value  http   underscorejs org  has   has object  key

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As of now there is no direct method like string empty to check whether a string is empty or not  But in your code you can use a wrapper check for an empty string like      considering the variable in which your string is saved is named str   if  str  amp  amp  str length gt 0           Your code here which you want to run if the string is not empty       Using this you can also make sure that string is not undefined or null too  Remember  undefined  null and empty are three different things

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I use a combination  and the fastest checks are first   function isBlank pString        if   pString    pString length    0            return true               Checks for a non-white space character        which I think  citation needed  is faster        than removing all the whitespace and checking        against an empty string     return      s    test pString

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Don t assume that the variable you check is a string  Don t assume that if this var has a length  then it s a string   The thing is  think carefully about what your app must do and can accept  Build something robust   If your method   function should only process a non empty string then test if the argument is a non empty string and don t do some  trick    As an example of something that will explode if you follow some advices here not carefully    var getLastChar   function  str     if  str length   0     return str charAt str length - 1     getLastChar  hello       o   getLastChar  0 1 2 3      TypeError  Object  object Array  has no method  charAt     So  I d stick with   if  myVar

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Starting with   return   value    value    undefined    value          value length    0     Looking at the last condition  if value        its length must be 0  Therefore drop it   return   value    value    undefined    value           But wait  In JavaScript  an empty string is false  Therefore  drop value         return   value    value    undefined     And  undefined is true  so that check isn t needed  So we have   return   value     And we don t need parentheses   return  value

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I usually use something like   if  str                 Do Something   else          Do Something Else

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A lot of answers  and a lot of different possibilities  Without a doubt for quick and simple implementation the winner is  if   str length        However  as many other examples are available  The best functional method to go about this  I would suggest   x000D   x000D  function empty str        if  typeof str     undefined      str    str length     0    str                s   test str        s    test str     str replace   s g                     return true      else         return false    x000D   x000D   x000D   A bit excessive  I know

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Performance  I perform tests on macOS v10 13 6  High Sierra  for 18 chosen solutions  Solutions works slightly different  for corner-case input data  which was presented in the snippet below   Conclusions   the simple solutions based on  str        and length are fast for all browsers  A B C G I J  the solutions based on the regular expression  test replace  and charAt are slowest for all browsers  H L M P  the solutions marked as fastest was fastest only for one test run - but in many runs it changes inside  fast  solutions group     Details  In the below snippet I compare results of chosen 18 methods by use different input parameters       a     - empty string  string with letter and string with space       f- array  object and function 0 1 NaN Infinity - numbers true false - Boolean null undefined   Not all tested methods support all input cases    x000D   x000D  function A str    x000D    let r 1  x000D    if   str  x000D      r 0  x000D    return r  x000D    x000D   x000D  function B str    x000D    let r 1  x000D    if  str        x000D      r 0  x000D    return r  x000D    x000D   x000D  function C str    x000D    let r 1  x000D    if  str         x000D      r 0  x000D    return r  x000D    x000D   x000D  function D str    x000D    let r 1  x000D    if  str    0     str length  x000D      r 0  x000D    return r  x000D    x000D   x000D  function E str    x000D    let r 1  x000D    if  str       s    test str   x000D      r 0  x000D    return r  x000D    x000D   x000D  function F str    x000D    let r 1  x000D    if  Boolean str   x000D      r 0  x000D    return r  x000D    x000D   x000D  function G str    x000D    let r 1  x000D    if     typeof str     undefined    amp  amp  str    x000D      r 0  x000D    return r  x000D    x000D   x000D  function H str    x000D    let r 1  x000D    if    S  test str   x000D      r 0  x000D    return r  x000D    x000D   x000D  function I str    x000D    let r 1  x000D    if   str length  x000D      r 0  x000D    return r  x000D    x000D   x000D  function J str    x000D    let r 1  x000D    if str length  lt   0  x000D      r 0  x000D    return r  x000D    x000D   x000D  function K str    x000D    let r 1  x000D    if str length     0     str trim    x000D      r 0  x000D    return r  x000D    x000D   x000D  function L str    x000D    let r 1  x000D    if   str replace   s g            x000D      r 0  x000D    return r  x000D    x000D   x000D  function M str    x000D    let r 1  x000D    if     s     test str   x000D      r 0  x000D    return r  x000D    x000D   x000D   x000D  function N str    x000D    let r 1  x000D    if  str     str trim   length  x000D      r 0  x000D    return r  x000D    x000D   x000D  function O str    x000D    let r 1  x000D    if  str     str trim    x000D      r 0  x000D    return r  x000D    x000D   x000D  function P str    x000D    let r 1  x000D    if  str charAt 0   x000D      r 0  x000D    return r  x000D    x000D   x000D  function Q str    x000D    let r 1  x000D    if  str     str trim         x000D      r 0  x000D    return r  x000D    x000D   x000D  function R str    x000D    let r 1  x000D    if  typeof str     undefined     x000D         str    x000D        str length     0    x000D        str           x000D             s   test str     x000D           s    test str     x000D        str replace   s g             x000D   x000D      r 0  x000D    return r  x000D    x000D   x000D   x000D   x000D   x000D     --- TEST --- x000D   x000D  console log                            a             0 1 NaN Infinity f true false null undefined     x000D  let log1    s f   gt  console log    s     f          f  a         f           f         f         f 0     f 1     f NaN       f Infinity            f f     f true        f false         f null        f undefined      x000D  let log2    s f   gt  console log    s     f          f  a         f           f         f         f 0     f 1     f NaN       f Infinity            f f     f true        f false      x000D  let log3    s f   gt  console log    s     f          f  a         f          x000D   x000D  log1  A   A   x000D  log1  B   B   x000D  log1  C   C   x000D  log1  D   D   x000D  log1  E   E   x000D  log1  F   F   x000D  log1  G   G   x000D  log1  H   H   x000D   x000D  log2  I   I   x000D  log2  J   J   x000D   x000D  log3  K   K   x000D  log3  L   L   x000D  log3  M   M   x000D  log3  N   N   x000D  log3  O   O   x000D  log3  P   P   x000D  log3  Q   Q   x000D  log3  R   R   x000D   x000D   x000D    And then for all methods I perform speed test case str      for browsers Chrome v78 0 0  Safari v13 0 4  and Firefox v71 0 0 - you can run tests on your machine here

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check that var a  exist trim out the false spaces in the value  then test for emptiness  if   a  amp  amp  a trim                if variable a is not empty do this

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Trimming whitespace with the null-coalescing operator  if   str  trim           do something

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I have not noticed an answer that takes into account the possibility of null characters in a string  For example  if we have a null character string   var y     0      an empty string  but has a null character  y            false  testing against an empty string does not work  y length     0     false  y     true  this is also not expected  y match     s          false  again not wanted   To test its nullness one could do something like this   String prototype isNull   function       return Boolean this match     0                 0  isNull      true   It works on a null string  and on an empty string and it is accessible for all strings  In addition  it could be expanded to contain other JavaScript empty or whitespace characters  i e  nonbreaking space  byte order mark  line paragraph separator  etc

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You can check this using the typeof operator along with the length method  const isEmptyString    value    gt  typeof value      string   amp  amp  value length  gt  0

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in case of checking the empty string simply if  str length       do something    if you also want to include null  amp  undefined with your check simply if  Boolean str        this will be true when the str is not empty nor null nor undefined

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All these answers are nice   But I cannot be sure that variable is a string  doesn t contain only spaces  this is important for me   and can contain  0   string    My version   function empty str       return  str         s    test str      empty null      true empty 0      true empty 7      false empty         true empty  0       false empty           true   Sample on jsfiddle

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There s no isEmpty   method  you have to check for the type and the length   if  typeof test      string   amp  amp  test length     0           The type check is needed in order to avoid runtime errors when test is undefined or null

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I prefer to use not blank test instead of blank   function isNotBlank str       return  str  amp  amp     s    test str

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Try this  str value length    0

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if   str  trim    length    0   gt  0          str must not be any of        undefined       null        quot  quot         quot   quot  or just whitespace    Update  Since this answer is getting popular I thought I d write a function form too  const isNotNilOrWhitespace   input   gt   input  trim    length    0   gt  0   const isNilOrWhitespace   input   gt   input  trim    length    0      0

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lt html gt       lt head gt           lt script lang  javascript  gt               function nullcheck                                 var n    fdgdfg                   var e   n length                  if  e    0                                        return true                                    else                                       alert  success                        return false                                           lt  script gt       lt  head gt        lt body gt           lt button type  submit  value  add  onclick  nullcheck    gt  lt  button gt       lt  body gt   lt  html gt

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Ignoring whitespace strings  you could use this to check for null  empty and undefined   var obj          obj str     Returns false  obj str          obj str     Returns false  obj str   null     obj str     Returns false   It is concise and it works for undefined properties  although it s not the most readable

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Try this   export const isEmpty   string   gt    string     string length

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It s a good idea too to check that you are not trying to pass an undefined term   function TestMe       if  typeof str     undefined    amp  amp  str        alert str            TestMe     var str    hello    TestMe      I usually run into the case where I want to do something when a string attribute for an object instance is not empty   Which is fine  except that attribute is not always present

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An alternative way  but I believe bdukes s answer is best   var myString    hello    if myString charAt 0        alert  no empty      alert  empty

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You can easily add it to native String object in JavaScript and reuse it over and over    Something simple like below code can do the job for you if you want to check    empty strings   String prototype isEmpty   String prototype isEmpty    function       return     this length       Otherwise if you d like to check both    empty string and       with space  you can do that by just adding trim    something like the code below   String prototype isEmpty   String prototype isEmpty    function        return     this trim   length       and you can call it this way      isEmpty      return true  alireza  isEmpty      return false

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I use   function empty e      switch  e        case         case 0      case  0       case null      case false      case typeof e      undefined         return true      default        return false         empty null     true empty 0     true empty 7     false empty        true empty  function         return           false

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If you just want to check whether there s any value  you can do   if  strValue          do something     If you need to check specifically for an empty string over null  I would think checking against    is your best bet  using the     operator  so that you know that it is  in fact  a string you re comparing against    if  strValue

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The following regular expression is another solution  that can be used for null  empty or undefined string      null undefined       test null    I added this solution  because it can be extended further to check empty or some value like as follow  The following regular expression is checking either string can be empty null undefined or it has integers only      null undefined      d      test

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var s     undefined var s             s length    0   There s nothing representing an empty string in JavaScript  Do a check against either length  if you know that the var will always be a string  or against

[javascript] How can I check for an empty/undefined/null string in JavaScript?

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