Javascript null or empty string does not work

Question

I am trying to test that my string is null or empty, however it does not work.

My Code :

var veri = {
  YeniMusteriEkleTextBox: $('#MyTextbox').val(),
};

if (veri.YeniMusteriEkleTextBox === "" || 
    veri.YeniMusteriEkleTextBox == '' || 
    veri.YeniMusteriEkleTextBox.length == 0 || 
    veri.YeniMusteriEkleTextBox == null) {
  alert("Customer Name can not be empty!!!");
}

How can ı check YeniMusteriEkleTextBox is null or empty ?

Where is this code located? Inside of a `document ready` handler? — contradictioned, Sep 12 '13 at 13:03
Notice that `'' === ""` and that checking for `.length == 0` was equivalent when you did knew that it was a string — Bergi, Sep 12 '13 at 13:06

score 4 · Answer 1 · answered Sep 12 '13 at 13:02

I would use the ! operator to test if it is empty, undefined etc.

if (!veri.YeniMusteriEkleTextBox) {
    alert("Customer Name can not be empty!!!");
}

Also you do not need the comma after YeniMusteriEkleTextBox: $('#MyTextbox').val(),

Also testing for a length on an object that may be undefined will throw an error as the length will not be 0, it will instead be undefined.

score 2 · Answer 2 · answered Sep 13 '13 at 06:45

You need to .trim the value to remove leading and trailing white space:

var veri = {
    YeniMusteriEkleTextBox: $('#YeniMusteriAdiTextbox_I').val().trim()
};

The .trim method doesn't exist on some older browsers, there's a shim to add it at the above MDN link.

You can then just test !veri.YeniMusteriEkleTextBox or alternatively veri.YeniMusteriEkleTextBox.length === 0:

if (!veri.YeniMusteriEkleTextBox) {
    alert("Customer Name can not be empty!!!");
}

score 1 · Answer 3 · edited May 23 '17 at 12:06

1

You should use

if (!veri.YeniMusteriEkleTextBox) {

This also checks for undefined which is not the same as null

edited May 23 '17 at 12:06

Community

1
1

answered Sep 12 '13 at 13:05

micha

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Additionally OP, if `YeniMusteriEkleTextBox` was `null`, your code would have a runtime exception as `null` does not have the property `length`. When using `null`/`undefined` checks, make sure those occur first as they are (1) the fastest and (2) minimize risk of runtime exceptions as we see here. – Jaime Torres Sep 12 '13 at 13:16

score -1 · Answer 4 · answered Sep 13 '13 at 06:54

Since no one else is suggestion $.trim, I will

Note I removed the trailing comma too and use the ! not operator which will work for undefined, empty null and also 0, which is not a valid customer name anyway

var veri = {
  YeniMusteriEkleTextBox: $.trim($('#MyTextbox').val())
};

if (!veri.YeniMusteriEkleTextBox) {
  alert("Customer Name can not be empty!!!");
}

Javascript null or empty string does not work

4 Answers4

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