How to check 'undefined' value in jQuery

> 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
}

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.

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.

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
}

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.

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

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')
    }
  })

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.

I am not sure it is the best solution, but it works fine:

if($someObject['length']!=0){
    //do someting
}

function isValue(value, def, is_return) {
    if ( $.type(value) == 'null'
        || $.type(value) == 'undefined'
        || $.trim(value) == ''
        || ($.type(value) == 'number' && !$.isNumeric(value))
        || ($.type(value) == 'array' && value.length == 0)
        || ($.type(value) == 'object' && $.isEmptyObject(value)) ) {
        return ($.type(def) != 'undefined') ? def : false;
    } else {
        return ($.type(is_return) == 'boolean' && is_return === true ? value : true);
    }
}

try this~ all type checker

Check if undefined or not

if(typeof myVal === "undefined") {
   //some code
}

Check if undefined or null or empty or false or 0

if(!myVal) {
   // some code
} else {
   // myVal is flawless 
}