Linked Questions
35 questions linked to/from How can I check for an undefined or null variable in JavaScript?
-1
votes
3
answers
34k
views
how to check document.getElementbyId contains null or undefined value in it? [duplicate]
if(typeof (document.getElementById("courseId").value!=="undefined") || document.getElementById("courseId").value!==null)
{
Courseid = document.getElementById("courseId").value;
}
- 93
-2
votes
1
answer
10k
views
Typescript - checking for null and undefined the easy way [duplicate]
I'm working on an Angular 11 project and I'm struggling with checking for null and undefined.
I have three strings - equipmentId, roomId and personnelId and a flag (boolean) adresseeChosen.
I want the ...
-1
votes
3
answers
896
views
check for undefined variable [duplicate]
Possible Duplicate:
How to check for undefined or null variable in javascript
I want to check for an defined variable in javascript. Please see the following few examples and help me which is the ...
- 33.4k
-1
votes
3
answers
1k
views
!=null or !=undefined not working [duplicate]
I'm trying to create a personalized welcome message on the homepage, that basically says "welcome [username]" providing the user has registered and their username goes into localStorage. That works ...
- 87
0
votes
3
answers
360
views
How can I trigger this 'typeof(undefined) != undefined' error? Undefined doesn't do the trick... JS [duplicate]
I have a function:
function goError(thing){
console.log(typeof(thing)); //RETURNS A STRING 'UNDEFINED'
if(typeof(thing) != undefined){
console.log(thing); //RETURNS UNDEFINED
...
- 11.1k
2
votes
5
answers
145
views
Recommended way to spot undefined variable which have been declared [duplicate]
For detect undefined variable which have been declared in javascript there at least two different ways.
var bar; // declared variable
if (typeof bar !== "undefined") {
// make something with ...
- 14.3k
0
votes
3
answers
179
views
Undefined variable in Javascript: difference between typeof and not exists [duplicate]
I don't understand the difference between these two ways of checking if a variable is undefined:
if (typeof res.locals.user.hashnodes === 'undefined') {
morphemes = 0;
}
and
if (!res.locals....
- 8,614
-2
votes
2
answers
121
views
best way to check if something is null or undefined [duplicate]
I was wondering, what's the best way to check if something is null or undefined in JSON arrays or objects in general? For years i've been using
if (value !== null && value !== undefined) {
/...
4154
votes
56
answers
5.9m
views
How do I check for an empty/undefined/null string in JavaScript?
Is there a string.Empty in JavaScript, or is it just a case of checking for ""?
- 70.1k
3248
votes
49
answers
1.5m
views
Detecting an undefined object property
How do I check if an object property in JavaScript is undefined?
- 118k
2717
votes
33
answers
3.5m
views
How can I determine if a variable is 'undefined' or 'null'?
How do I determine if a variable is undefined or null?
My code is as follows:
var EmpName = $("div#esd-names div#name").attr('class');
if(EmpName == 'undefined'){
// DO SOMETHING
};
<...
- 41k
180
votes
6
answers
87k
views
Why is NaN not equal to NaN? [duplicate]
The relevant IEEE standard defines a numeric constant NaN (not a number) and prescribes that NaN should compare as not equal to itself. Why is that?
All the languages I'm familiar with implement this ...
- 52.7k
185
votes
8
answers
526k
views
JavaScript null check
I've come across the following code:
function test(data) {
if (data != null && data !== undefined) {
// some code here
}
}
I'm somewhat new to JavaScript, but, from other ...
- 5,206
80
votes
6
answers
261k
views
Undefined or null for AngularJS
When I write watch handling functions I check newVal param on undefined and null. Why does AngularJS have such a behavior, but doesn't have particular utility method? So there is angular.isUndefined ...
- 1,009
27
votes
8
answers
63k
views
How can I check if a localstorage variable is null or undefined?
I have this code:
var sideBar = localStorage.getItem('Sidebar');
I want to check if sideBar is defined and not null in an if statement. I am a bit confused I know there's a: sideBar == undefined and ...
user1679941