Count number of words in string using JavaScript

[edit 2022, based on comment] Nowadays, one would not extend the native prototype this way. A way to extend the native protype without the danger of naming conflicts is to use the es20xx symbol. Here is an example of a wordcounter using that.

Old answer: you can use split and add a wordcounter to the String prototype:

if (!String.prototype.countWords) {
  String.prototype.countWords = function() {
    return this.length && this.split(/\s+\b/).length || 0;
  };
}

console.log(`'this string has five words'.countWords() => ${
  'this string has five words'.countWords()}`);
console.log(`'this string has five words ... and counting'.countWords() => ${
  'this string has five words ... and counting'.countWords()}`);
console.log(`''.countWords() => ${''.countWords()}`);

I would prefer a RegEx only solution:

var str = "your long string with many words.";
var wordCount = str.match(/(\w+)/g).length;
alert(wordCount); //6

The regex is

\w+    between one and unlimited word characters
/g     greedy - don't stop after the first match

The brackets create a group around every match. So the length of all matched groups should match the word count.

This is the best solution I've found:

function wordCount(str) { var m = str.match(/[^\s]+/g) return m ? m.length : 0; }

This inverts whitespace selection, which is better than \w+ because it only matches the latin alphabet and _ (see http://www.ecma-international.org/ecma-262/5.1/#sec-15.10.2.6)

If you're not careful with whitespace matching you'll count empty strings, strings with leading and trailing whitespace, and all whitespace strings as matches while this solution handles strings like ' ', ' a\t\t!\r\n#$%() d ' correctly (if you define 'correct' as 0 and 4).