I want to know what the difference is between null and undefined in JavaScript....

Which method of checking if a variable has been initialized is better/correct? (Assuming the variable could hold anything (string, int, object, function, etc.))  if (elem) { // or !elem   or  if (typeof(elem) !== 'undefined') {   or  if (el...

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?...

I have a global variable in JavaScript (actually a window property, but I don't think it matters) which was already populated by a previous script but I don't want another script that will run later to see its value or that it was even defi...

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...

I wanted to check whether the variable is defined or not. For example, the following throws a not-defined error    alert( x );   How can I catch this error?...

I am trying to access this inside my arrow function:  import myObject from '../myObjectPath'; export const myClass = Fluxxor.createStore({     initialize() {         this.list = [];         this.id = null;     },     myOutsideFunction(varia...

Recently I installed node.js on my Windows 7 machine.   On execution of JavaScript, I get an undefined message along with successful execution of the expression.   What's wrong here? I have not noticed any other side effects....

Hi I have the 3 javascript files.   jquery.js utility.js file1.js   In file1.js I have   jQuery.noConflict() jQuery(document).ready(function($) {   // .... });   I get an error 'jQuery' was used before it was defined.  and 'document'...

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