How to check if a text is all white space characters in client side?

How to check if a user input text is all white space characters (space, tab, enter etc) in client side?

This question is tagged with jQuery. In jQuery, you can run the following:

if ( $.trim( $('#myInput').val() ) == '' )
    alert('input is blank');

/^\s+$/.test(userText)

Change the + to * to include the empty string '' as a positive match.

Edit

More often than not though you need to trim whitespace from user-entered text and simply test if it's non-empty:

userText = userText.replace(/^\s+/, '').replace(/\s+$/, '');
if (userText === '') {
    // text was all whitespace
} else {
    // text has real content, now free of leading/trailing whitespace
}

This will also work:

var text = "   ";
text.trim().length == 0; //true