How to check undefined value in jQuery

Question

Possible Duplicate    Detecting an undefined object property in JavaScript   javascript undefined compare       How we can add a check for an undefined variable  like   function A val      if  val    undefined          do this   else        do this

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Note that typeof always returns a string  and doesn t generate an error if the variable doesn t exist at all   function A val     if typeof val        undefined          do this   else      do this

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if  value     undefined

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If you have names of the element and not id we can achieve the undefined check on all text elements  for example  as below and fill them with a default value say 0 0   var aFieldsCannotBeNull   ast chkacc bwr   ast savacc bwr     jQuery each aFieldsCannotBeNull function nShowIndex sShowKey       var   oField   jQuery  input name    sShowKey           if   oField val   trim   length     0            oField val  0 0

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I am not sure it is the best solution  but it works fine   if  someObject  length    0         do someting

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I know I am late to answer the function but jquery have a in build function to do this   if jQuery type val       undefined          Some code goes here     Refer jquery API document of jquery type https   api jquery com jQuery type  for the same

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when I am testing  typeof obj     undefined   the alert typeof obj  returning object  even though obj is undefined  Since obj is type of Object its returning Object  not undefined   So after hours of testing I opted below technique   if document getElementById obj      null     do     else    do        I am not sure why the first technique didn t work But I get done my work using this

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In this case you can use a     undefined comparison  if val     undefined   This works because val always exists  it s a function argument    If you wanted to test an arbitrary variable that is not an argument  i e  might not be defined at all  you d have to use if typeof val      undefined   to avoid an exception in case val didn t exist

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You can use two way 1  if   val    null   2  if   val     undefine

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JQuery library was developed specifically to simplify and to unify certain JavaScript functionality   However if you need to check a variable against undefined value  there is no need to invent any special method  since JavaScript has a typeof operator  which is simple  fast and cross-platform   if  typeof value      undefined                    It returns a string indicating the type of the variable or other unevaluated operand  The main advantage of this method  compared to if  value     undefined           is that typeof will never raise an exception in case if variable value does not exist

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You can use shorthand technique to check whether it is undefined or null   function A val        if val              do this  else    do this      hope this will help you

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function isValue value  def  is return        if     type value      null               type value      undefined               trim value                      type value      number   amp  amp     isNumeric value                 type value      array   amp  amp  value length    0                type value      object   amp  amp    isEmptyObject value               return    type def      undefined     def   false        else           return    type is return      boolean   amp  amp  is return     true   value   true             try this  all type checker

[javascript] How to check 'undefined' value in jQuery

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