How to check if a variable is null or empty string or all whitespace in JavaScript?

Question

I need to check to see if a variable is null or has all empty spaces or is just blank (\"\").

I have the following, but it is not working:

var addr;
         


        

Answer 1

When checking for white space the c# method uses the Unicode standard. White space includes spaces, tabs, carriage returns and many other non-printing character codes. So you are better of using:

function isNullOrWhiteSpace(str){
    return str == null || str.replace(/\s/g, '').length < 1;
}

Answer 2

You can use if(addr && (addr = $.trim(addr)))

This has the advantage of actually removing any outer whitespace from addr instead of just ignoring it when performing the check.

Reference: http://api.jquery.com/jQuery.trim/

Answer 3

You can try this:

do {
   var op = prompt("please input operatot \n you most select one of * - / *  ")
} while (typeof op == "object" || op == ""); 
// execute block of code when click on cancle or ok whthout input

Answer 4

Simplified version of the above: (from here: https://stackoverflow.com/a/32800728/47226)

function isNullOrWhitespace( input ) {
  return !input || !input.trim();
}

Answer 5

isEmptyOrSpaces(str){
    return str === null || str.trim().length>0;
}

Answer 6

Old question, but I think it deservers a simpler answer.

You can simply do:

var addr = "  ";

if (addr && addr.trim()) {

    console.log("I'm not null, nor undefined, nor empty string, nor string composed of whitespace only.");

}