[javascript] 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
}

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
}

You can use two way 1) if ( val == null ) 2) if ( val === undefine )

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

if (value === undefined) {
    // ...
}

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

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

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.

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.

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')
    }
  })