jQuery: checking if the value of a field is null (empty)

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Is this a good way to check if the value of a field is null?

if($('#person_data[document_type]').value() != 'NULL'){}

Or is there a better way?

The value of a field can not be null, it's always a string value.

The code will check if the string value is the string "NULL". You want to check if it's an empty string instead:

if ($('#person_data[document_type]').val() != ''){}

or:

if ($('#person_data[document_type]').val().length != 0){}

If you want to check if the element exist at all, you should do that before calling val:

var $d = $('#person_data[document_type]');
if ($d.length != 0) {
  if ($d.val().length != 0 ) {...}
}

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I would also trim the input field, cause a space could make it look like filled

if ($.trim($('#person_data[document_type]').val()) != '')
{

}

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Assuming

var val = $('#person_data[document_type]').value();

you have these cases:

val === 'NULL';  // actual value is a string with content "NULL"
val === '';      // actual value is an empty string
val === null;    // actual value is null (absence of any value)

So, use what you need.

jQuery.isEmptyObject(), In JS, an empty string is false. And !undefined is true, so that check isn't needed . This checks if the type of the value is "string" (and thus non-null and not not be what you want if you wanted to throw an error for an unexpected input type. Answer: Use the jQuery val() Method You can use the val() method to test or check if inputs are empty in jQuery. The following example will add a red outline around the inputs if it is focused but not filled out.

that depends on what kind of information are you passing to the conditional..

sometimes your result will be null or undefined or '' or 0, for my simple validation i use this if.

( $('#id').val() == '0' || $('#id').val() == '' || $('#id').val() == 'undefined' || $('#id').val() == null )

NOTE: null != 'null'

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_helpers: {
        //Check is string null or empty
        isStringNullOrEmpty: function (val) {
            switch (val) {
                case "":
                case 0:
                case "0":
                case null:
                case false:
                case undefined:
                case typeof this === 'undefined':
                    return true;
                default: return false;
            }
        },

        //Check is string null or whitespace
        isStringNullOrWhiteSpace: function (val) {
            return this.isStringNullOrEmpty(val) || val.replace(/\s/g, "") === '';
        },

        //If string is null or empty then return Null or else original value
        nullIfStringNullOrEmpty: function (val) {
            if (this.isStringNullOrEmpty(val)) {
                return null;
            }
            return val;
        }
    },

Utilize this helpers to achieve that.

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How to check empty/undefined/null string in JavaScript , Hi guys, what I'm trying to accomplish is. when the textarea is empty it will show a specific button. but when the textarea has value it will show ano. i try to put text on the textarea it will allert not null, but when i remove the text it won't alert null. If you are working on jquery and However you want to check variable is undefined or not then you can easily check by typeof operator, which is simple, fast and cross-platform: if(typeof i == "undefined") {

Comments
  • what kind of element is #person_data? and what do you consider as a NULL value?
  • stackoverflow.com/a/49923589/7186739
  • The value of a field can not be null, it's always a string value. this isn't entirely true. I've got a select containing no options. When I perform .val() on this it returns null. Jquery 1.7.2
  • @Pispirulito: I don't think so, and I don't think that it will be changed. A select without any option elements is not something that you normally have. It's pretty useless.
  • @Guffa beg to differ, an empty <select> can contain possible options for your user whose <option>s will come from some sort of validation.
  • If you use the following solution to provide a placeholder in your select, it will start out with a null value because a 'disabled' option is selected. stackoverflow.com/questions/5805059/…
  • this almost seems like isStringNullOrEmpty is isStringFalsey and thus return !val; would work