I want to know what the difference is between null and undefined in JavaScript....
Why is null considered an object in JavaScript?  Is checking   if ( object == null )       Do something   the same as   if ( !object )       Do something   ?  And also:  What is the difference between null and undefined?...
We are frequently using the following code pattern in our JavaScript code  if (typeof(some_variable) != 'undefined' && some_variable != null) {     // Do something with some_variable }   Is there a less verbose way of checking that...
How can I check for null values in JavaScript? I wrote the code below but it didn't work.  if (pass == null || cpass == null || email == null || cemail == null || user == null) {            alert("fill all columns");     return false;...
As you may know, in JavaScript '' + null = "null" and '' + undefined = "undefined" (in most browsers I can test: Firefox, Chrome and IE). I would like to know the origin of this oddity (what the heck was in the head on...
How do I verify the existence of an object in JavaScript?  The following works:  if (!null)    alert("GOT HERE");   But this throws an Error:  if (!maybeObject)    alert("GOT HERE");   The Error:      maybeObject is not defined....
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 questions I've been reading here, I'...
I'm using a system to alert users when a major update has happened to a site, and I do it with LocalStorage, when I made the system, I made the system check if tip was "null", then set "tip" to true when they got the alert. Now, I...
While trying to debug I am get the 'length' null error with this line.    It is written just like the book instructed, so I don't understand why it is giving me the error? Thanks, =)  if (capital.length < 1) {   ( here is the full code...
null and undefined don't have a toString or valueOf method. Afaik using String calls the toString method of its parameter (e.g. String({}) => [object Object]).   Why do String(null) or String(undefined work then? It doesn't implicitly do O...

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