Dec 4, 2014 · What would be a good way to test Javascript on a browser? Should there be a localhost in my computer? and how to create one?

The in operator checks for the existence of a property, regardless of its value, while the question at least appears to be asking how to test if the value of a variable is undefined.

Many times I'm using the string match function to know if a string matches a regular expression.

As many know, (0 == "") is true in JavaScript, but since 0 is a value and not empty or null, you may want to test for it. The following two functions return true only for undefined, null, empty/whitespace values …

How can I determine whether a variable is a string or something else in JavaScript?

Feb 6, 2009 · Edit: If you were working in front-end Javascript and you needed to check if a variable was not initialized (var x = undefined would count as not initialized), you could use:

In order to understand, Let's analyze what will be the value return by the Javascript Engine when converting undefined , null and '' (An empty string also). You can directly check the same on your …

Aug 26, 2008 · How do I check if an object property in JavaScript is undefined?

Jun 22, 2009 · Here is a function that uses a regular expression to test against the letters of a string; it returns true if the letter is uppercase (A-Z). We then reduce the true/false array to a single value.

Mar 25, 2009 · After an AJAX request, sometimes my application may return an empty object, like: var a = {}; How can I check whether that's the case?