How can I check for an empty/undefined/null string in JavaScript?

Question

I saw this question, but I didn't see a JavaScript specific example. Is there a simple string.Empty available in JavaScript, or is it just a case of checking for ""?

Answer 1

If you just want to check whether there's a truthy value, you can do:

if (strValue) {     //do something } 

If you need to check specifically for an empty string over null, I would think checking against "" is your best bet, using the === operator (so that you know that it is, in fact, a string you're comparing against).

if (strValue === "") {     //... } 

Answer 2

For checking if a variable is falsey or if it has length attribute equal to zero (which for a string, means it is empty), I use:

function isEmpty(str) {     return (!str || str.length === 0 ); } 

_{(Note that strings aren't the only variables with a length attribute, arrays have them as well, for example.)}

For checking if a variable is falsey or if the string only contains whitespace or is empty, I use:

function isBlank(str) {     return (!str || /^\s*$/.test(str)); } 

If you want, you can monkey-patch the String prototype like this:

String.prototype.isEmpty = function() {     // This doesn't work the same way as the isEmpty function used      // in the first example, it will return true for strings containing only whitespace     return (this.length === 0 || !this.trim()); }; console.log("example".isEmpty()); 

_{Note that monkey-patching built-in types is controversial, as it can break code that depends on the existing structure of built-in types, for whatever reason.}