Is there a standard function to check for null, undefined, or blank variables in JavaScript?

Question

Is there a universal JavaScript function that checks that a variable has a value and ensures that it\'s not undefined or null? I\'ve got this code,

Answer 1

A solution I like a lot:

Let's define that a blank variable is null, or undefined, or if it has length, it is zero, or if it is an object, it has no keys:

function isEmpty (value) {
  return (
    // null or undefined
    (value == null) ||

    // has length and it's zero
    (value.hasOwnProperty('length') && value.length === 0) ||

    // is an Object and has no keys
    (value.constructor === Object && Object.keys(value).length === 0)
  )
}

Returns:

• true: undefined, null, "", [], {}
• false: true, false, 1, 0, -1, "foo", [1, 2, 3], { foo: 1 }

Answer 2

Here's mine - returns true if value is null, undefined, etc or blank (ie contains only blank spaces):

function stringIsEmpty(value) {

    return value ? value.trim().length == 0 : true;

}

Answer 3

function isEmpty(val){
    return !val;
}

but this solution is over-engineered, if you dont'want to modify the function later for busines-model needings, then is cleaner to use it directly in code:

if(!val)...

Answer 4

For everyone coming here for having similar question, the following works great and I have it in my library the last years:

(function(g3, $, window, document, undefined){
   g3.utils = g3.utils || {};
/********************************Function type()********************************
* Returns a lowercase string representation of an object's constructor.
* @module {g3.utils}
* @function {g3.utils.type}
* @public
* @param {Type} 'obj' is any type native, host or custom.
* @return {String} Returns a lowercase string representing the object's 
* constructor which is different from word 'object' if they are not custom.
* @reference http://perfectionkills.com/instanceof-considered-harmful-or-how-to-write-a-robust-isarray/
* http://stackoverflow.com/questions/3215046/differentiating-between-arrays-and-hashes-in-javascript
* http://javascript.info/tutorial/type-detection
*******************************************************************************/
g3.utils.type = function (obj){
   if(obj === null)
      return 'null';
   else if(typeof obj === 'undefined')
      return 'undefined';
   return Object.prototype.toString.call(obj).match(/^\[object\s(.*)\]$/)[1].toLowerCase();
};
}(window.g3 = window.g3 || {}, jQuery, window, document));

Answer 5

If the variable hasn't been declared, you wont be able to test for undefined using a function because you will get an error.

if (foo) {}
function (bar) {}(foo)

Both will generate an error if foo has not been declared.

If you want to test if a variable has been declared you can use

typeof foo != "undefined"

if you want to test if foo has been declared and it has a value you can use

if (typeof foo != "undefined" && foo) {
    //code here
}

Answer 6

It may be usefull.

All values in array represent what you want to be (null, undefined or another things) and you search what you want in it.

var variablesWhatILookFor = [null, undefined, ''];
variablesWhatILookFor.indexOf(document.DocumentNumberLabel) > -1