is there something like isset of php in javascript jQuery

Question

Is there something in javascript jQuery to check whether variable is set available or not  In php  we use isset  variable  to check something like this   thanks

User · Answer

typeof will serve the purpose I think  if typeof foo     undefined

User · Answer

in addition to  emil-vikstr  m s answer  checking for variable  null would be true for variable   null as well as for variable   undefined  or typeof variable    undefined

User · Answer

Not naturally  no    However  a googling of the thing gave this  http   phpjs org functions isset 454

User · Answer

Some parts of each of these answers work  I compiled them all down into a function  isset  just like the question was asking and works like it does in PHP       isset helper function  var isset   function variable       return typeof variable       undefined   amp  amp  variable     null  amp  amp  variable              Here is a usage example of how to use it   var example    this is an example   if isset example        console log  the example variable has a value set        It depends on the situation you need it for but let me break down what each part does    typeof variable       undefined  checks if the variable is defined at all variable     null checks if the variable is null  some people explicitly set null and don t think if it is set to null that that is correct  in that case  remove this part  variable        checks if the variable is set to an empty string  you can remove this if an empty string counts as set for your use case   Hope this helps someone

User · Answer

The problem is that passing an undefined variable to a function causes an error   This means you have to run typeof before passing it as an argument   The cleanest way I found to do this is like so   function isset v       if v      undefined            return false            return true      Usage   if isset typeof varname       alert  is set      else     alert  not set        Now the code is much more compact and readable   This will still give an error if you try to call a variable from a non instantiated variable like   isset typeof undefVar subkey     thus before trying to run this you need to make sure the object is defined   undefVar   isset typeof undefVar   undefVar

User · Answer

Here     function isSet iVal    return  iVal       amp  amp  iVal  null  amp  amp  iVal   undefined  amp  amp  typeof iVal      undefined     1   0       Returns 1 if set  0 false

User · Answer

Try this expression   typeof variable      undefined   amp  amp  variable     null   This will be true if the variable is defined and not null  which is the equivalent of how PHP s isset works   You can use it like this   if typeof variable      undefined   amp  amp  variable     null        bla

User · Answer

JavaScript isset   on PHP JS  function isset             discuss at  http   phpjs org functions isset            original by  Kevin van     Zonneveld  http   kevin vanzonneveld net             improved by  FremyCompany            improved by  Onno Marsman            improved by  Rafal Kukawski              example 1  isset  undefined  true                returns 1  false              example 2  isset   Kevin van Zonneveld                  returns 2  true     var a   arguments          l   a length          i   0          undef       if  l     0            throw new Error  Empty isset               while  i     l            if  a i      undef    a i      null                return false                    i              return true

User · Answer

If you want to check if a property exists  hasOwnProperty is the way to go  And since most objects are properties of some other object  eventually leading to the window object  this can work well for checking if values have been declared

User · Answer

You can just   if variable  variable   0         Yes it is set       do something   else         No it is not set       Or its null       do something else

User · Answer

http   phpjs org functions isset 454  phpjs project is a trusted source  Lots of js equivalent php functions available there  I have been using since a long time and found no issues so far

[javascript] is there something like isset of php in javascript/jQuery?

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