JavaScript: What is the best way to test for an empty string?

If you only want to test, if a variable has any value, you can do it like this:

if (str) {
   alert('OK');
}

If you want to test, whether it is also a variable of the type String, you can proceed as follows:

if (str === '') {
   alert('OK');
}

The comparison operator with three equal signs tests on the one hand on the same content and on the other hand on the same type (in this case string); compared with ==, which only checks for the same content.
2012-01-26 at 21:43

You can also look at the length of the string, like this:

if (str.length == 0) {
   alert('String is empty.');
}

Or even more elegant:

if (!str.length) {
   alert('String is empty.');
}

There are certainly many ways...
2012-01-28 at 17:14

I think the best solution is the following, so we can also see if our string is null:

if (!!str) {
   alert('Empty String!');
}

Only that works for me for a string that is undefined, null or empty.
2012-01-28 at 17:09

If we want to treat even strings that contain only white space, such as spaces or line breaks, as empty, we can do it like this:

if ((/^\s*$/).test(str)) {
   alert('emtpy string or only whitespace');
}

Of course, this is obviously something heavier in performance, than the other suggested solutions.
2012-01-31 at 21:37