Editing prototype of String

Question

This is my code:

String.prototype.count = function(character) {
    var seq = new RegExp('/'+character+'/g');
    var matches = this.toString().match(seq);
    return matches
};

'hello world'.count('o');

This is what it should do:

Return array of os

This is what it's doing:

Return null

That's not how you create regex with the RegExp constructor, check the docs here https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp — elclanrs, Oct 01 '14 at 05:49
possible duplicate of [How to count string occurrence in string?](http://stackoverflow.com/questions/4009756/how-to-count-string-occurrence-in-string) — Phil, Oct 01 '14 at 05:53
Also, your method is named very poorly. I would expect a method named `count` to return a single integer. — Phil, Oct 01 '14 at 05:55

score 1 · Accepted Answer · answered Oct 01 '14 at 05:51

String.prototype.count = function(character) {
    var seq = new RegExp(character, 'g');
    var matches = this.toString().match(seq);
    return matches;
};

alert('hello world'.count('o'));

ps: if you do not want to use regexps in character - you should escape it.

score 0 · Answer 2 · answered Oct 01 '14 at 05:52

You're not creating the RegExp that you want. It should be:

    var seq = new RegExp(character, 'g');

When you use the RegExp constructor, you just give it the contents of the regular expression, you don't need the / delimiters -- those are only used in RegExp literals. Your RegExp is looking for the literal string /o/g.

Editing prototype of String

This is what it should do:

This is what it's doing:

2 Answers2