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...
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?...
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'...
I was using console.log() in some JavaScript I wrote and an error of: console is not defined was thrown in Internet Explorer (worked fine in other browsers).  I have replaced it with:  if (console) console.log("...");  If console is undefined...
I am in a situation that needs be solve with this way; need convert a local variable to a global variable. There is an example returning image's real width and height which i found these method from this answer..  Need to convert local varialbes...
It appears that window.undefined is writable, i.e. it can be set to something else than its default value (which is, unsurprisingly, undefined).  The point is however that whenever I refer to undefined, it refers to window.undefined (as window can be...
On this page, it shows some example code, containing the following line:  var Subject = ( function( window, undefined ) {   What is the undefined as a function parameter?...

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