Determine whether a string is "empty"

Question

I need a JavaScript function to tell me whether a string object is empty. By "empty", I mean that it's not all just whitespace characters. I've written this prototype:

String.prototype.isEmpty = function() {
  return this.length === 0 || this === " " || this.test(/^\s*$/);
}

Is this alright?

Is there a more-performant version of this out there?

Answer 1

It looks like you need to use /^\s*$/.test(this) instead of this.test(/^\s*$/). There is no test() method for strings, unless you're using some JavaScript library that implements this method.

The /^\s*$/.test(this) would have been enough, but the first two expressions would short circuit if any one of them evaluates to true, without having to test the regular expression. That should be pretty efficient.

As @Matthew Crumley noted in a comment above, your this === " " expression will always evaluate to false. You could remove this expression, or use == if you would will be expecting a lot of strings with just a single space character:

String.prototype.isEmpty = function() {
  return this.length === 0 || this == " " || /^\s*$/.test(this);
}

Answer 2

String.prototype.isEmpty = function() {
  return this.length == 0 || /^\s*$/.test(this);
}

There is just a possibility out of 255 (not considering Unicode characters with code greater than 255) that a string with length 1 contains the space character. Considering strings with lenght greater than 1, the possibility get even lower.

Answer 3

Use

String.prototype.isEmpty = function() {  
  if (!this.match(/\S/)) {
    return ('enter some valid input.Empty space is not allowed');
  } else {
   return "correct input";
  }
}


alert("test 1:"+("    ".isEmpty()));
alert("test 2:"+("   \t ".isEmpty()));
alert("test 3:"+("  \n   ".isEmpty()));
alert("test 4:"+("hi".isEmpty()));

Note:

\s will match a whitespace character: space, tab or new line.

\S will match non whitespace character:anything but not a space, tab or new line. If your string has a single character which is not a space, tab or new line, then it's not empty. Therefore you just need to search for one character: \S

Answer 4

I fiddled with some of the things:

• I'm returning the inverse of this.length, for 0 that is true, for everything other number that is false.
• I removed the check for " ". I actually haven't seen much, if any cases where a single space was entered, removing the check is IMO faster on average.
• And flipped the regex <-> string like the others did.

String.prototype.isEmpty = function() {
return !this.length || /^\s*$/.test(this);
}

Answer 5

Generally, using RegExp.prototype.test for checking for a pattern match without compilation of a return array of matches (String.prototype.match) likely has a better performance. I'd try -- but haven't tested yet -- something like:

function isEmpty() {

     var string = arguments[0] ;
     var EMPTY_STRING_PATTERN = /^\s*$/ , empty = false ;

     if( EMPTY_STRING_PATTERN.exec(string) === true ) empty = true ;

     return empty ;

}

On a side note, it is considered bad practice to fiddle with the prototype object of core javascript objects.

Answer 6

from example https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/String/Trim

var orig="   foo  "
document.write(orig.trim())  // foo

document.write(orig.trim().length) // 3

tested on FF 3.6.8, Safari 5.0.1, Google Chrome 5.0.375.127, but produce js error on IE 8