Checking something isEmpty in Javascript

Question

How can I check if a variable is empty in Javascript  Sorry for the stupid question  but I m a newbie in Javascript   if response photo  is empty       do something else       do something else     response photo was from JSON  and it could be empty sometimes  empty data cells  I want to check if it s empty

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Combining answers from  inkednm into one function      function isEmpty property          return  property     null    property           typeof property      undefined

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It depends on what you mean by  empty    The most common pattern is to check to see if the variable is undefined   Many people also do a null check  for example  if  myVariable     undefined    myVariable     null      or  in a shorter form  if  myVariable    myVariable     null

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if  myVar    undefined    will work to see if the var is declared but not initalized

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Here s a simpler short  solution to check for empty variables  This function checks if a variable is empty  The variable provided may contain mixed values  null  undefined  array  object  string  integer  function    function empty mixed var     if   mixed var    mixed var     0       return true      if  typeof mixed var     object       for  var k in mixed var       return false        return true      return false          example 1  empty null        returns 1  true       example 2  empty undefined        returns 2  true       example 3  empty           returns 3  true       example 4  empty           returns 4  true       example 5  empty 0        returns 5  true       example 6  empty  0         returns 6  true       example 7  empty function            returns 7  false

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A more readable version of  SJ00 answer         Checks if a JavaScript value is empty     example       isEmpty null      true       isEmpty undefined      true       isEmpty         true       isEmpty         true       isEmpty         true     param  any  value - item to test     returns  boolean  true if empty  otherwise false     function isEmpty value        return           value     null       check for null         value     undefined       check for undefined         value              check for empty string          Array isArray value   amp  amp  value length     0        check for empty array          typeof value      object   amp  amp  Object keys value  length     0     check for empty object

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const isEmpty   val   gt  val    null      Object keys val     val  length

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Check for undefined   if  typeof response photo     undefined            do something     This would do the equivelant of vb s IsEmpty   If myvar contains any value  even null  empty string  or 0  it is not  empty    To check if a variable or property exists  eg it s been declared  though it may be not have been defined  you can use the in operator   if   photo  in response           do something

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This is a bigger question than you think  Variables can empty in a lot of ways  Kinda depends on what you need to know      quick and dirty will be true for     null  undefined  0  NaN and false  if   x       test for null OR undefined if  x    null        test for undefined OR null  if  x    undefined       test for undefined if  x     undefined      or safer test for undefined since the variable undefined can be set causing tests against it to fail  if  typeof x     undefined        test for empty string if  x              if you know its an array if  x length    0       or if   x length      BONUS test for empty object var empty   true  fld  for  fld in x      empty   false    break

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x000D   x000D  function isEmpty variable    x000D    const type   typeof variable x000D    if  variable     null  return true x000D    if  type      undefined   return true x000D    if  type      boolean   return false x000D    if  type      string   return  variable x000D    if  type      number   return false x000D    if  Array isArray variable   return  variable length x000D    if  type      object   return  Object keys variable  length x000D    return  variable x000D    x000D   x000D   x000D

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I see potential shortcomings in many solutions posted above  so I decided to compile my own  Note  it uses Array prototype some  check your browser support   Solution below considers variable empty if one of the following is true    JS thinks that variable is equal to false  which already covers many things like 0          and even      and  0  Value is null or it s type is  undefined  It is an empty Object  It is an Object Array consisting only of values that are empty themselves  i e  broken down to primitives each part of it equals false   Checks drill recursively into Object Array structure  E g    isEmpty      0      true isEmpty      1      false isEmpty               true isEmpty      0   0  false      true    Function code          Checks if value is empty  Deep-checks arrays and objects    Note  isEmpty        true  isEmpty        true  isEmpty   0 false     0      true  isEmpty  0 1      false     param value     returns  boolean      function isEmpty value     var isEmptyObject   function a        if  typeof a length      undefined        it s an Object  not an Array       var hasNonempty   Object keys a  some function nonEmpty element           return  isEmpty a element                    return hasNonempty   false   isEmptyObject Object keys a               return  a some function nonEmpty element       check if array is really not empty as JS thinks       return  isEmpty element      at least one element should be non-empty                return       value    false        typeof value      undefined         value    null         typeof value      object   amp  amp  isEmptyObject value

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If you re testing for an empty string   if myVar             do stuff      If you re checking for a variable that has been declared  but not defined   if myVar     null      do stuff      If you re checking for a variable that may not be defined   if myVar     undefined      do stuff      If you re checking both i e  either variable is null or undefined   if myVar    null      do stuff

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what am I missing if empty array    keyless object    falseness const isEmpty   o    Array isArray o   amp  amp   o join     length    typeof o      object   amp  amp   Object keys o  length       value

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See 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

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just put the variable inside the if condition  if variable has any value it will return true else false    if  response photo      if you are checking for string use this if response photo        condition  alert  Has Value      else    alert  No Value

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Here my simplest solution       Inspired by PHP empty function    x000D   x000D  function empty n   x000D   return     n   typeof n      object    Array isArray n      n length     Object keys n  length   true   false   x000D    x000D   x000D    with number x000D  console log empty 0             true x000D  console log empty 10            false x000D   x000D    with object x000D  console log empty               true x000D  console log empty  a  a         false x000D   x000D    with array x000D  console log empty               true x000D  console log empty  1 2          false x000D   x000D    with string x000D  console log empty               true x000D  console log empty  a            false x000D   x000D   x000D

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What about doing like this   JSON stringify

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If you re looking for the equivalent of PHP s empty function  check this out   function empty mixed var           example 1  empty null          returns 1  true        example 2  empty undefined          returns 2  true        example 3  empty             returns 3  true        example 4  empty             returns 4  true        example 5  empty   aFunc    function      alert  humpty                 returns 5  false    var undef  key  i  len    var emptyValues    undef  null  false  0       0       for  i   0  len   emptyValues length  i  lt  len  i          if  mixed var     emptyValues i           return true               if  typeof mixed var      object         for  key in mixed var             TODO  should we check for own properties only          if  mixed var hasOwnProperty key           return false                      return true         return false      http   phpjs org functions empty 392

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Empty check on a JSON s key depends on use-case  For a common use-case  we can test for following    Not null Not undefined Not an empty String    Not an empty Object        Array is an Object    Function   function isEmpty arg     return       arg    null       Check for null or undefined     arg length     0       Check for empty String  Bonus check for empty Array       typeof arg      object   amp  amp  Object keys arg  length     0     Check for empty Object or Array          Return true for   isEmpty         Empty String isEmpty null      null isEmpty       undefined isEmpty         Empty Object isEmpty         Empty Array

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This should cover all cases   function empty  val             test results       ---------------                  true  empty array                  true  empty object        null      true        undefined true                  true  empty string                  true  empty string        0         false  number        true      false  boolean        false     false  boolean        Date      false        function  false          if  val     undefined          return true       if  typeof  val      function     typeof  val      number     typeof  val      boolean     Object prototype toString call val        object Date            return false       if  val    null    val length     0            null or 0 length array         return true       if  typeof  val      object                empty object          var r   true           for  var f in val              r   false           return r             return false

[javascript] Checking something isEmpty in Javascript?

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