What is the best way to check for an empty string in JavaScript?

Question

I saw this thread, but I didn't see a JavaScript specific example. Is there a simple string.Empty in JavaScript, or is it just checking for "" ?

Answer 1

I usually compare to "" in Javascript.

Answer 2

If you just want to check whether there's any value, you can do

if (strValue) {
    //do something
}

If you need to check specifically for an empty string over null, I would think checking against "" is your best bet, using the === operator (so that you know that it is, in fact, a string you're comparing against).

Answer 3

I would say check against "".

Answer 4

I would not worry too much about the most efficient method. Use what is most clear to your intention. For me that's usually strVar == "".

EDIT: per comment from Constantin, if strVar some how ended up containing an integer 0 value, then strVar == "" returns true. So if that is a danger in your situation, you should code strVar === "", which ensures that the types are also the same.

Answer 5

var s; // undefined
var s = ""; // ""
s.length // 0

There's nothing representing an empty string in JavaScript. Do a check against either length (if you know that the var will always be a string) or against ""

Answer 6

The closest thing you can get to str.Empty (with the precondition that str is a String) is:

if (!str.length) { ...

Answer 7

If you need to make sure that the string is not just a bunch of empty spaces (I'm assuming this is for form validation) you need to do a replace on the spaces.

if(str.replace(/\s/g,"") == ""){
}

Answer 8

just FYI, i think the most useful APIs for the String class are at Mozilla and javascript kit. elated.com has a tutorial on all of String's properties, methods,...

Answer 9

thtx i'was searching for this only , solved my prob :
by this

if(str.replace(/\s/g,"") == ""){
}

Answer 10

I usually use something like:

if (str == "") {
     //Do Something
}
else {
     //Do Something Else
}

Answer 11

you could also go with regexps:

if((/^\s*$/).test(str)) { }

Checks for strings that are either empty or filled with whitespace.

Answer 12

I use :

function empty(e) {
                    switch(e) {
                        case "":
                        case 0:
                        case "0":
                        case null:
                        case false:
                        case typeof this == "undefined":
                            return true;
                                default : return false;
                    }
                }

empty(null) // true
empty(0) // true
empty(7) // false
empty("") // true
empty((function() { return "" }) ) // true

Answer 13

For checking if a string is empty, null or undefined I use:

function isEmpty(str) {
    return (!str || 0 === str.length);
}

For checking if a string is blank, null or undefined I use:

function isBlank(str) {
    return (!str || /^\s*$/.test(str));
}

Answer 14

str.value.length == 0

Answer 15

function tell()
{
var pass = document.getElementById('pasword').value;
var plen = pass.length;

now you can check if your string is empty as like 
if(plen==0)
{
         alert('empty');
}
else
{
   alert('you entered something');
}
}


<input type='text' id='pasword' />

this is also a generic way to check if field is empty.