Iam using following lines of code to check whether the JS variable 'userName' is null or not.
But am always getting alert "not empty"
Please check my onready method:
$("document").ready(function (){
var userName = "";
if (userName == undefined || userName == null) {
alert('empty');
} else {
alert('not empty');
var div = document.getElementById('title b');
div.innerHTML = div.innerHTML + ',';
}
});
You need typeof keyword to check it's type. !userName will take care of the rest, like null or empty values.
if ( typeof userName === 'undefined' || !userName ) {
alert('empty');
}
=== here, because the return of typeof is always a string and == is faster in this case ;)
!undefined is true anyways?userName gets initialized as an empty string, thus not undefined. But we never know what is going on behind the scenes.You're setting var userName to "". It will never be null.
Declare your variable as var userName;, instead of var userName = "";
However, unless you actually do something with userName, the if / else will be pretty pointless.
null in a JSON string will be parsed as null, not as an empty string, indeed.if(userName == null)No your variable is neither undefined nor null.
What you could do though is this replace this line
if (userName == undefined || userName == null) {
by this line
if (!userName) {
Empty string is not null nor undefined.
You can check using the ! operator:
if (!userName) {
// Do the stuff
}
For completeness:
!"" == true
!null == true
!undefined == true
!"hi" == false
Note that:
!0 == true
!1 == false
!"0" == false
!"1" == false
userName happens to be 0, !userName will be true; !1 -> false. Don't just cast the username to a boolean like that.Try
var userName = "";
if (userName.length < 1) {
alert('empty' +"\n"+ userName.length);
} else {
alert('not empty');
var div = document.getElementById('title b');
div.innerHTML = div.innerHTML + ',';
}
