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//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=0; 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