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

There are at least four ways. The best option, which should also be the fastest -owing to the native RegEx engine -, is placed at the top. jsperf.com is currently down, otherwise I would provide you with performance statistics.

Update: Please, find the performance tests here, and run them yourselves, so as to contribute your performance results. The specifics of the results will be given later.

1.

 ("this is foo bar".match(/o/g)||[]).length
 //>2

2.

"this is foo bar".split("o").length-1
 //>2

split not recommended. Resource hungry. Allocates new instances of 'Array' for each match. Don't try that for a >100MB file via FileReader. You can actually easily observe the EXACT resource usage using Chrome's profiler option.

3.

var stringsearch = "o"
   ,str = "this is foo bar";
for(var count=-1,index=-2; index != -1; count++,index=str.indexOf(stringsearch,index+1) );
 //>count:2

4.

searching for a single character

var stringsearch = "o"
   ,str = "this is foo bar";
for(var i=count=0; icount:2

Update:

5.

element mapping and filtering, not recommended due to its overall resource preallocation rather than using Pythonian 'generators'

var str = "this is foo bar"
str.split('').map( function(e,i){ if(e === 'o') return i;} )
             .filter(Boolean)
//>[9, 10]
[9, 10].length
//>2

Share: I made this gist, with currently 8 methods of character-counting, so we can directly pool and share our ideas - just for fun, and perhaps some interesting benchmarks :)

https://gist.github.com/2757250