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?.

Yes. I found this short note in the MDN site: If you need to know if a string matches a regular expression regexp, use regexp.test (string). Is the difference significant? The answer once more is YES! This …

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.

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?

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.

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.