How to check whether the input text field contains only white spaces?

What is the easiest way to check in Javascript whether the input text field is empty (开发者_运维问答contains nothing or white spaces only)?

var str = document.getElementById("myInput").value;
if (str.match(/^\s*$/)) {
    // nothing, or nothing but whitespace
} else {
    // something
}

You are looking for something like trim function, right?

Include this function somewhere (in order to provide a trim function)

String.prototype.trim = function () {
   return this.replace(/^\s*(\S*(\s+\S+)*)\s*$/, "$1");
};

see here http://javascript.crockford.com/remedial.html

then...

if (document.forms['id_of_form'].elements['id_of_input'].value.trim()=='') {
    //do xyz
}