Count the number of occurrences of a character in a string in Javascript

Question

I need to count the number of occurrences of a character in a string.

For example, suppose my string contains:

var mainStr = \"str1,str2,str3,str4\";         


        

Answer 1

I was working on a small project that required a sub-string counter. Searching for the wrong phrases provided me with no results, however after writing my own implementation I have stumbled upon this question. Anyway, here is my way, it is probably slower than most here but might be helpful to someone:

function count_letters() {
var counter = 0;

for (var i = 0; i < input.length; i++) {
    var index_of_sub = input.indexOf(input_letter, i);

    if (index_of_sub > -1) {
        counter++;
        i = index_of_sub;
    }
}

http://jsfiddle.net/5ZzHt/1/

Please let me know if you find this implementation to fail or do not follow some standards! :)

UPDATE You may want to substitute:

    for (var i = 0; i < input.length; i++) {

With:

for (var i = 0, input_length = input.length; i < input_length; i++) {

Interesting read discussing the above: http://www.erichynds.com/blog/javascript-length-property-is-a-stored-value