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?

May 13, 2009 · This is not a duplicate of the marked duplicate. Variable resolution and object property resolution are very different things. A better duplicate is how to check if a variable exist in javascript?.

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.

Is there a string.Empty in JavaScript, or is it just a case of checking for ""?

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

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:

All arrays are objects, so checking the constructor property is a fast process for JavaScript engines. If you are having issues with finding out if an objects property is an array, you must first check if the …

Sep 5, 2017 · If myvar is 0, false or any other falsy value the test will fail (if you only intend to check for not null). So only use this to check for not null if the variable can never have another falsy value.

Aug 25, 2015 · Here's a jsfiddle to test it out, and in particular it includes some jQuery that breaks if you modify the Object.prototype directly because of the property becoming enumerable.