Is there a standard function to check for null undefined or blank variables in JavaScript

Question

Is there a universal JavaScript function that checks that a variable has a value and ensures that it s not undefined or null  I ve got this code  but I m not sure if it covers all cases   function isEmpty val       return  val     undefined    val    null    val length  lt   0    true   false

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If you prefer plain javascript try this              Checks if  value  is empty  Arrays  strings  or  arguments  objects with a      length of  0  and objects with no own enumerable properties are considered       empty              static       memberOf         category Objects       param  Array Object string  value The value to inspect        returns  boolean  Returns  true  if the  value  is empty  else  false         example             isEmpty  1  2  3              gt  false             isEmpty                gt  true             isEmpty                gt  true             isEmpty                gt  true        function isEmpty value        if   value          return true            if  isArray value     isString value           return  value length            for  var key in value          if  hasOwnProperty call value  key             return false                    return true        Otherwise  if you are already using underscore or lodash  try     isEmpty value

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You are a bit overdoing it  To check if a variable is not given a value  you would only need to check against undefined and null   function isEmpty value       return  typeof value      undefined     value     null       This is assuming 0      and objects even empty object and array  are valid  values

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The optional chaining operator provides a way to simplify accessing values through connected objects when it s possible that a reference or function may be undefined or null   let customer       name   Carl     details        age  82      location   Paradise Falls     detailed address is unknown        let customerCity   customer details  address  city    The nullish coalescing operator may be used after optional chaining in order to build a default value when none was found   let customer       name   Carl     details    age  82      const customerCity   customer  city     Unknown city   console log customerCity      Unknown city

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For everyone coming here for having similar question  the following works great and I have it in my library the last years    function g3     window  document  undefined      g3 utils   g3 utils                                         Function type                                     Returns a lowercase string representation of an object s constructor     module  g3 utils     function  g3 utils type     public    param  Type   obj  is any type native  host or custom     return  String  Returns a lowercase string representing the object s    constructor which is different from word  object  if they are not custom     reference http   perfectionkills com instanceof-considered-harmful-or-how-to-write-a-robust-isarray    http   stackoverflow com questions 3215046 differentiating-between-arrays-and-hashes-in-javascript   http   javascript info tutorial type-detection                                                                                  g3 utils type   function  obj      if obj     null        return  null      else if typeof obj      undefined         return  undefined      return Object prototype toString call obj  match     object s          1  toLowerCase         window g3   window g3        jQuery  window  document

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This covers empty Array and empty Object also     null  undefined       0             isEmpty    value    gt    value      typeof v      object   amp  amp     Object keys value  length  lt  1

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This condition check  if    foo          foo is defined     is all you need

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try        let vari   obj propTest     obj may be don t have propTest property                catch NullException          do something here     I think using try catch will avoid any error of null check  also in Angular or JavaScript Just catching null exception and process in it

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check for empty strings       null  undefined  false and the number 0 and NaN  Say  if a string is empty var name      then console log  name  returns true   function isEmpty val     return  val      this function will return true if val is empty  null  undefined  false  the number 0 or NaN   OR  According to your problem domain you can just use like  val or   val

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This will check if variable of indeterminate nesting is undefined  function Undef str       var ary   str split         var w   window    for  i in ary        try        if  typeof w   w ary i         undefined   return true        catch e    return true          return false     if   Undef  google translate TranslateElement        The above checks if the Google translate function TranslateElement exists   This is equivalent to   if    typeof google      undefined       typeof google translate      undefined       typeof google translate TranslateElement      undefined

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This is the safest check and I haven t seen it posted here exactly like that   if  typeof value      undefined   amp  amp  value          deal with value       It will cover cases where value was never defined  and also any of these    null undefined  value of undefined is not the same as a parameter that was never defined  0     empty string  false NaN   Edited  Changed to strict equality       because it s the norm by now

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A solution I like a lot   Let s define that a blank variable is null  or undefined  or if it has length  it is zero  or if it is an object  it has no keys   function isEmpty  value      return          null or undefined      value    null             has length and it s zero      value hasOwnProperty  length    amp  amp  value length     0             is an Object and has no keys      value constructor     Object  amp  amp  Object keys value  length     0          Returns    true  undefined  null             false  true  false  1  0  -1   foo    1  2  3     foo  1

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function notEmpty value     return  typeof value      undefined   amp  amp  value trim   length       it will also check white spaces          along with following    null  undefined  NaN  empty  string       0  false

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You can directly use the equality operator   lt script gt      var firstName      var lastName   null         Since null    undefined is true  the following statements will catch both null and undefined            if firstName    null               alert  Variable  firstName  is undefined                           if lastName    null              alert  Variable  lastName  is null                lt  script gt    demo   How to determine if variable is undefined or null using JavaScript

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function isEmpty val       return  val      but this solution is over-engineered  if you dont want to modify the function later for busines-model needings  then is cleaner to use it directly in code   if  val

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Most of the existing answers failed for my use case  most returned empty if a function was assigned to the variable or if NaN was returned  Pascal s answer was good   Here s my implementation  please test and let me know if you find anything  You can see how I tested this function here   function isEmpty value      return          Null or undefined       value    null            Check if a Set   or Map   is empty      value size     0            NaN - The only JavaScript value that is unequal to itself       value     value            Length is zero  amp  amp  it s not a function       value length     0  amp  amp  typeof value      function             Is an Object  amp  amp  has no keys       value constructor     Object  amp  amp  Object keys value  length     0          Returns    true  undefined  null              NaN  new Set       false  true  false  1  0  -1   foo    1  2  3     foo  1    function

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Although an oldie  what forget is that they should wrap their code block and then catch the error and then test     function checkup  t      try      for p in t         if  p hasOwnProperty  t              return true                    return false     catch e       console log  ERROR     e       return e          So you really don t have to check for a potential problem before hand  you simply catch it and then deal with it how you want

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If the variable hasn t been declared  you wont be able to test for undefined using a function because you will get an error    if  foo     function  bar     foo    Both will generate an error if foo has not been declared   If you want to test if a variable has been declared you can use  typeof foo     undefined    if you want to test if foo has been declared and it has a value you can use  if  typeof foo     undefined   amp  amp  foo          code here

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You may find the following function useful    function typeOf obj      return    toString call obj  split      1  slice 0  -1  toLowerCase        Or in ES7  comment if further improvements   function typeOf obj      const   toString     Object prototype    const stringified   obj  toString      const type   stringified split      1  slice 0  -1      return type toLowerCase        Results   typeOf      undefined typeOf null     null typeOf NaN     number typeOf 5     number typeOf        object typeOf        array typeOf        string typeOf function           function typeOf  a     regexp typeOf new Date      date typeOf new WeakMap      weakmap typeOf new Map      map    Note that the bind operator      is not part of ES2016  ES7  nor any later edition of the ECMAScript standard at all  It s currently a stage 0  strawman  proposal for being introduced to the language       Simon Kjellberg  the author wishes to add his support for this beautiful proposal to receive royal ascension

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To check Default Value  function typeOfVar  obj          return    toString call obj  split      1  slice 0  -1  toLowerCase      function isVariableHaveDefaltVal variable        if   typeof variable       string          number  boolean  string  object          console log   Any data Between single double Quotes is treated as String                     return  variable trim   length     0    true   false       else if   typeof variable       boolean            console log  boolean value with default value   false              return  variable     false    true   false       else if   typeof variable       undefined              console log  EX  var a  variable is created  but has the default value of undefined              return true       else if   typeof variable       number               console log  number     variable           return  variable     0     true   false       else if   typeof variable       object              -----Object-----         if  typeOfVar variable       array   amp  amp  variable length     0                console log   t Object Array with length          length      Object keys variable              return true           else if  typeOfVar variable       string   amp  amp  variable length     0                 console log   t Object String with length       variable length               return true           else if  typeOfVar variable       boolean                  console log   t Object Boolean       variable               return  variable     false    true   false           else if  typeOfVar variable       number                  console log   t Object Number       variable               return  variable     0     true   false           else if  typeOfVar variable       regexp   amp  amp  variable source trim   length     0            console log   t Object Regular Expression               return true           else if  variable     null           console log   t Object null value            return true                      return false    var str    A Basket For Every Occasion   str   str replace   s g   -      The  g  flag in the regex will cause all spaces to get replaced    check Result   isVariableHaveDefaltVal          string           isVariableHaveDefaltVal false      boolean        var a             isVariableHaveDefaltVal a                  isVariableHaveDefaltVal 0      number              isVariableHaveDefaltVal parseInt          NAN isNAN       - true          isVariableHaveDefaltVal null                 isVariableHaveDefaltVal                     isVariableHaveDefaltVal                     isVariableHaveDefaltVal new Object                      isVariableHaveDefaltVal new Object false                isVariableHaveDefaltVal new Object 0     typeOfVar  function           I used  Vix function   to check the object of which type   using instansof     var prototypes or Literals   function  obj        switch  typeof obj                object prototypes         case  object               if  obj instanceof Array                  return   object Array                else if  obj instanceof Date                  return   object Date                else if  obj instanceof RegExp                  return   object regexp                else if  obj instanceof String                  return   object String                else if  obj instanceof Number                  return   object Number                 else                 return  object              object literals         default              return typeof obj               output test    prototypes or Literals           string  prototypes or Literals  new String            object String   Object prototype toString call  foo bar       object String

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you can use the arguments become arguments to array filter   x000D   x000D  function validateAttrs arg1  arg2  arg3 arg4       var args   Object values arguments       return  args filter x  gt  x   null     x   length lt  0   console log validateAttrs  1  2  3  4    console log validateAttrs  1  2  3  null    console log validateAttrs  1  undefined  3  4    console log validateAttrs  1  2      4    console log validateAttrs  1  2  3  null    x000D   x000D   x000D

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It may be usefull   All values in array represent what you want to be  null  undefined or another things  and you search what you want in it   var variablesWhatILookFor    null  undefined       variablesWhatILookFor indexOf document DocumentNumberLabel   gt  -1

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Here s mine - returns true if value is null  undefined  etc or blank  ie contains only blank spaces    function stringIsEmpty value         return value   value trim   length    0   true

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This function check for empty object    empty array     null  undefined and blank string     function isEmpty val        check for empty object     array      if  val     null  amp  amp  typeof val      object         if  Object keys obj  length     0          return true                check for undefined  null and       else if  val    null    val               return true        return false         var val        isEmpty val  -    true   val       isEmpty val  -    true   isEmpty undefined  -  true   isEmpty null  -  true   isEmpty     -  true   isEmpty false  -  false   isEmpty 0  -  false

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I think using the   operator is slightly cleaner   var   function if exists     function if doesnt exist

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Will return false only for undefined and null  return value    false

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Take a look at the new ECMAScript Nullish coalescing operator   You can think of this feature - the    operator - as a way to    fall back    to a default value when dealing with null or undefined   let x   foo    bar        Again  the above code is equivalent to the following   let x    foo     null  amp  amp  foo     undefined    foo   bar

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you can always use loadash functions  like   nil or   undefined  They are pretty good to use

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var myNewValue   myObject  amp  amp  myObject child  amp  amp  myObject child myValue    This will never throw an error  If myObject  child  or myValue is null then myNewValue will be null  No errors will be thrown

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The probably shortest answer is  val  null    val       if you change rigth side to val      then empty array will give false  Proof    x000D   x000D  function isEmpty val   x000D      return val  null    val     x000D    x000D   x000D     ------------ x000D     TEST x000D     ------------ x000D   x000D  var log    name val    gt  console log    name  - gt    isEmpty val      x000D   x000D  log  null   null   x000D  log  undefined   undefined   x000D  log  NaN   NaN   x000D  log            x000D  log            x000D  log            x000D  log   1     1    x000D  log   0     0    x000D  log                x000D  log  true   true   x000D  log  false   false   x000D  log   true     true    x000D  log   false     false    x000D  log  Infinity   Infinity   x000D  log  -Infinity   -Infinity   x000D  log  1   1   x000D  log  0   0   x000D  log  -1   -1   x000D  log   1     1    x000D  log   0     0    x000D  log   -1     -1    x000D   x000D      void 0  case x000D  console log  --- n true  is    true   x000D  console log   void 0  is    void 0   x000D  log void 0 void 0       void 0  is  undefined  - so we should get here TRUE x000D   x000D   x000D    More details about     source here     BONUS  Reason why     is more clear than        To write clear and  easy  understandable  code  use explicite list of accepted values  val   undefined    val   null    val         Array isArray val   amp  amp  val length   0     x000D   x000D  function isEmpty val   x000D      return val   undefined    val   null    val          Array isArray val   amp  amp  val length   0  x000D    x000D   x000D     ------------ x000D     TEST x000D     ------------ x000D   x000D  var log    name val    gt  console log    name  - gt    isEmpty val      x000D   x000D  log  null   null   x000D  log  undefined   undefined   x000D  log  NaN   NaN   x000D  log            x000D  log            x000D  log            x000D  log   1     1    x000D  log   0     0    x000D  log                x000D  log  true   true   x000D  log  false   false   x000D  log   true     true    x000D  log   false     false    x000D  log  Infinity   Infinity   x000D  log  -Infinity   -Infinity   x000D  log  1   1   x000D  log  0   0   x000D  log  -1   -1   x000D  log   1     1    x000D  log   0     0    x000D  log   -1     -1    x000D   x000D      void 0  case x000D  console log  --- n true  is    true   x000D  console log   void 0  is    void 0   x000D  log void 0 void 0       void 0  is  undefined  - so we should get here TRUE x000D   x000D   x000D

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Vacuousness I don t recommend trying to define or use a function which computes whether any value in the whole world is empty  What does it really mean to be  empty   If I have  let human     name   bob   stomach   empty      should  isEmpty human   return  true   If I have  let reg   new RegExp        should  isEmpty reg   return  true   What about  isEmpty   null  null  null  null     - this list only contains emptiness  so is the list itself empty  I want to put forward here some notes on  vacuousness   an intentionally obscure word  to avoid pre-existing associations  in javascript - and I want to argue that  vacuousness  in javascript values should never be dealt with generically   Truthiness Falsiness For deciding how to determine the  vacuousness  of values  we need to accomodate javascript s inbuilt  inherent sense of whether values are  truthy  or  falsy   Naturally   null  and  undefined  are both  falsy   Less naturally  the number  0   and no other number except  NaN   is also  falsy   Least naturally       is falsy  but      and       and  new Set     and  new Map     are truthy - although they all seem equally vacuous   Null vs Undefined There is also some discussion concerning  null  vs  undefined  - do we really need both in order to express vacuousness in our programs  I personally avoid ever having the letters u  n  d  e  f  i  n  e  d appear in my code in that order  I always use  null  to signify  vacuousness   Again  though  we need to accomodate javascript s inherent sense of how  null  and  undefined  differ   Trying to access a non-existent property gives undefined Omitting a parameter when calling a function results in that parameter receiving undefined    x000D   x000D  let f   a   gt  a  console log f  hi     console log f     x000D   x000D   x000D    Parameters with default values receive the default only when given undefined  not null    x000D   x000D  let f    v  hello     gt  v  console log f null    console log f undefined    x000D   x000D   x000D    Non-generic Vacuousness I believe that vacuousness should never be dealt with in a generic fashion  We should instead always have the rigour to get more information about our data before determining if it is vacuous - I mainly do this by checking what type of data I m dealing with   x000D   x000D  let isType    value  Cls    gt         Intentional use of loose comparison operator detects  null       and  undefined   and nothing else    return value    null  amp  amp  Object getPrototypeOf value  constructor     Cls     x000D   x000D   x000D   Note that this function ignores polymorphism - it expects value to be a direct instance of Cls  and not an instance of a subclass of Cls  I avoid instanceof for two main reasons       instanceof Object      true     quot An Array is an Object quot       instanceof String      false    quot A String is not a String quot    Note that Object getPrototypeOf is used to avoid a case like let v     constructor  String    The isType function still returns correctly for isType v  String   false   and isType v  Object   true   Overall  I recommend using this isType function along with these tips   Minimize the amount of code processing values of unknown type  E g   for let v   JSON parse someRawValue    our v variable is now of unknown type  As early as possible  we should limit our possibilities  The best way to do this can be by requiring a particular type  e g  if   isType v  Array   throw new Error  Expected Array    - this is a really quick and expressive way to remove the generic nature of v  and ensure it s always an Array  Sometimes  though  we need to allow v to be of multiple types  In those cases  we should create blocks of code where v is no longer generic  as early as possible    x000D   x000D  if  isType v  String          v isn t generic in this block - It s a String       else if  isType v  Number          v isn t generic in this block - It s a Number       else if  isType v  Array          v isn t generic in this block - it s an Array       else     throw new Error  Expected String  Number  or Array      x000D   x000D   x000D    Always use  quot whitelists quot  for validation  If you require a value to be  e g   a String  Number  or Array  check for those 3  quot white quot  possibilities  and throw an Error if none of the 3 are satisfied  We should be able to see that checking for  quot black quot  possibilities isn t very useful  Say we write if  v     null  throw new Error  Null value rejected    - this is great for ensuring that null values don t make it through  but if a value does make it through  we still know hardly anything about it  A value v which passes this null-check is still VERY generic - it s anything but null  Blacklists hardly dispell generic-ness  Unless a value is null  never consider  quot a vacuous value quot   Instead  consider  quot an X which is vacuous quot   Essentially  never consider doing anything like if  isEmpty val                 - no matter how that isEmpty function is implemented  I don t want to know      it isn t meaningful  And it s way too generic  Vacuousness should only be calculated with knowledge of val s type  Vacuousness-checks should look like this    quot A string  with no chars quot   if  isType val  String   amp  amp  val length     0        quot An Object  with 0 props quot   if  isType val  Object   amp  amp  Object entries val  length     0        quot A number  equal or less than zero quot   if  isType val  Number   amp  amp  val  lt   0        quot An Array  with no items quot   if  isType val  Array   amp  amp  val length     0       The only exception is when null is used to signify certain functionality  In this case it s meaningful to say   quot A vacuous value quot   if  val     null

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Below worked for me  Please do a slight change to make this fast  function isEmpty obj        if   obj  return true      if  typeof obj     number   return false      else if  typeof obj     string   return obj length    0      else if  Array isArray obj   return obj length    0      else if  typeof obj     object   return obj    null    Object keys obj  length    0      else if  typeof obj     boolean   return false

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If you want to avoid getting true if the value is any of the following  according to jAndy s answer    null undefined NaN empty string      0 false   One possible solution that might avoid getting truthy values is the following   function isUsable valueToCheck        if  valueToCheck     0           Avoid returning false if the value is 0          valueToCheck                 Avoid returning false if the value is an empty string          valueToCheck     false       Avoid returning false if the value is false          valueToCheck                 Returns true if it isn t null  undefined  or NaN                return true        else           return false            It would be used as follows   if  isUsable x            It is usable       Make sure to avoid placing the logical NOT operator before the parameter  isUsable  x   and instead  use it before the function  to check the returned value  if   isUsable x            It is NOT usable        In addition to those scenarios  you may want to return false if the object or array is empty    Object      Using ECMA 7   Array      Using ECMA 5     You would go about it this way   function isEmptyObject valueToCheck        if typeof valueToCheck      object   amp  amp   Object keys valueToCheck  length              Object is empty          return true        else              Object is not empty          return false           function isEmptyArray valueToCheck        if Array isArray valueToCheck   amp  amp   valueToCheck length               Array is empty          return true        else              Array is not empty          return false            If you wish to check for all whitespace strings        you may do the following   function isAllWhitespace        if  valueToCheck match             null               Is all whitespaces          return true        else              Is not all whitespaces          return false              Note  hasOwnProperty returns true for empty strings  0  false  NaN  null  and undefined  if the variable was declared as any of them  so it might not be the best to use  The function may be modified to use it to show that it was declared  but is not usable

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Try With Different Logic  You can use bellow code for check all four 4  condition for validation like not null  not blank  not undefined and not zero only use this code      variable    in javascript and jquery   function myFunction         var data     The Values can be like as null  blank  undefined  zero you can test      if     data                  alert  data   data              else                alert  data is   data

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The first answer with best rating is wrong  If value is undefined it will throw an exception in modern browsers  You have to use    if  typeof value       undefined   amp  amp  value    or   if  typeof value       undefined   amp  amp  value

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If you are using TypeScript and don t want to account for  values those are false  then this is the solution for you                          First    import   isNullOrUndefined   from  util    Then     isNullOrUndefined this yourVariableName                     Please Note  As mentioned below this is now deprecated  use value     undefined    value     null instead  ref

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Try Boolean   and isNaN    for number type  to check a variable has a value or not   x000D   x000D  function isEmpty val      return typeof val      number    isNaN val     Boolean val      var emptyVals    undefined  null  false  NaN       emptyVals forEach v   gt  console log isEmpty v     x000D   x000D   x000D

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You can just check if the variable has a truthy value or not  That means  if  value         will evaluate to true if value is not    null undefined NaN empty string      0 false   The above list represents all possible falsy values in ECMA- Javascript  Find it in the specification at the ToBoolean section   Furthermore  if you do not know whether a variable exists  that means  if it was declared  you should check with the typeof operator  For instance  if  typeof foo      undefined             foo could get resolved and it s defined     If you can be sure that a variable is declared at least  you should directly check if it has a truthy value like shown above   Further read  http   typeofnan blogspot com 2011 01 typeof-is-fast html

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function isEmpty value     return  value    null    value length     0       This will return true for  undefined     Because undefined    null  null           and zero argument functions since a function s length is the number of declared parameters it takes   To disallow the latter category  you might want to just check for blank strings  function isEmpty value     return  value    null    value

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return val     Handle empty variable    is a really nice and clean way to handle it in a lot of places  can also be used to assign variables   const res   val     default value

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For my case I tried with if null      variable  But it did not work   See my code below to get the text from an html field  var status   this  text      for example  for my case    if there was no value no text  in the status variable  I was trying to set the value  novalue  to status variable    the following code worked   if status    false       status  novalue        when there was no text found for satus variable the above code assigned  novalue  to the status variable

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function isEmpty obj        if  typeof obj     number   return false      else if  typeof obj     string   return obj length    0      else if  Array isArray obj   return obj length    0      else if  typeof obj     object   return obj    null    Object keys obj  length    0      else if  typeof obj     boolean   return false      else return  obj      In ES6 with trim to handle whitespace strings   const isEmpty   value   gt        if  typeof value      number   return false     else if  typeof value      string   return value trim   length     0     else if  Array isArray value   return value length     0     else if  typeof value      object   return value    null    Object keys value  length     0     else if  typeof value      boolean   return false     else return  value

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The verbose method to check if value is undefined or null is   return value     undefined    value     null    You can also use the    operator but this expects one to know all the rules   return value    null     also returns true if value is undefined

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Code on GitHub  const isEmpty   value   gt        value  amp  amp  value     0  amp  amp  value     false        Array isArray value   amp  amp  value length     0        isObject value   amp  amp  Object keys value  length     0        typeof value size      number   amp  amp  value size     0         WeekMap length  is supposed to exist         typeof value length      number         amp  amp  typeof value      function   amp  amp  value length     0         Source  https   levelup gitconnected com javascript-check-if-a-variable-is-an-object-and-nothing-else-not-an-array-a-set-etc-a3987ea08fd7 const isObject   value   gt    Object prototype toString call value        object Object      Poor man s tests   const test        gt      const run    label  values  expected    gt        const length   values length      console group    label     length  tests         values map  v  i    gt          console assert isEmpty v      expected     i     v                 console groupEnd            const empty         null  undefined  NaN                  new Set    new Set      new Map    new Map             const notEmpty               a   0  1  -1  false  true   a  1    0       new Set  0    new Map    a   1         new WeakMap   set     1       new Date     a   new RegExp         gt             const shouldBeEmpty          undefined  undefined   new Map                run  EMPTY   empty  true     run  NOT EMPTY   notEmpty  false     run  SHOULD BE EMPTY   shouldBeEmpty  true        Test results   EMPTY  10 tests  NOT EMPTY  16 tests  SHOULD BE EMPTY  2 tests    Assertion failed  0   object Object    Assertion failed  1   object Map

[javascript] Is there a standard function to check for null, undefined, or blank variables in JavaScript?

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