//www.lsauer.com 2012
//Answer to:
//http://stackoverflow.com/questions/881085/count-the-number-of-occurances-of-a-character-in-a-string-in-javascript/10671743#10671743
//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.

#1.
     ("this is foo bar".match(/o/g)||[]).length
     //>2
#2.
    "this is foo bar".split("o").length-1
     //>2
//split is 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; i<str.length; count+=+(stringsearch===str[i++]));
     //>count:2


#5.
//element mapping and filtering; not recommended due to its overall resource pre-allocation vs. Pythonian 'generators'
//provides the position within the string
    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

#6
//'deleting' the character out of the string and measuring the distance in length
    var str = "this is foo bar";
    str.length - str.replace(/o/g,'').length
    //>2

#7
//based on typed arrays; str2buffer is taken from 'is-lib'; See: https://gist.github.com/lsauer
    //Converts an ASCII string to an typed-Array buffer
    str2buffer = function(s){ var bu = new ArrayBuffer(s.length), aUint8 = new Uint8Array(bu );
                              for(var i=0; i<bu.byteLength; aUint8[i]=s.charCodeAt(i),i++);return aUint8;
    };
    var bstr = str2buffer ("this is foo bar")
       ,schar = 'o'.charCodeAt()
       ,cnt=0;
    for(var i=0;i<bstr.byteLength;schar!==bstr[i++]||cnt++);
    //>cnt
    2
#8
//based on untyped Arrays. Is expected to be slower. Analogous to #7
    var ubstr = "this is foo bar".split('').map( function(e,i){ return e.charCodeAt();} )
       //>[116, 104, 105, 115, 32, 105, 115, 32, 102, 111, 111, 32, 98, 97, 114]
       ,schar = 'o'.charCodeAt()
       ,cnt=0;
    for(var i=0;i<ubstr.length;schar!==ubstr[i++]||cnt++);
    //>cnt
    2

#9
//using reduce. Note: Element map functions are powerful but slow as they involve their own heap/stack allocation
//see: http://stackoverflow.com/questions/10293378/what-is-the-most-efficient-way-of-merging-1-2-and-7-8-into-1-7-2-8/17910641#17910641
var str   = "this is foo bar",
    schar = 'o'; 
    str.split('').reduce( 
        function(p,c,i,a){ if(c === schar || p === schar){return isNaN(parseInt(p))? 1:+p+1;} return p;}
    ) 
//Note: faster: c === schar || p === schar; slower: (c+p).indexOf(schar)>-1

#10. dictionary character histogram
var str   = "this is foo bar",
    schar = 'o',
    hist={}; 
    for(si in str){
         hist[str[si]] = hist[str[si]] ? 1+hist[str[si]]:1;
    }
    //>hist[schar]
    2
    
//Changelog > 11/2013:
//
// 24/11/2013   #3 bug fixed in initial index position; pointed out by Augustus@Stackoverflow