function numInstring(str){

str=str.replace(/ /ig,"");
var strArr=str.split("");
var result=[],beforeLength,afterLength,reg;
for(var i=0;i<strArr.length;i++){
if(str.indexOf(strArr[i])!=-1){

beforeLength=str.length;

reg=new RegExp(strArr[i],"ig");

str=str.replace(reg,"");

afterLength=str.length;

result.push(strArr[i]+":"+(beforeLength-afterLength));

}

}
return result;

}

var result=numInstring("This section of the site is dedicated to the JavaScript language itself, the parts that are not specific to Web pages or other host");


console.log(result);

/*result:

["T:17", "h:7", "i:9", "s:10", "e:14", "c:5", "o:8", "n:3", "f:3", "d:3", "a:9", "J:1", "v:1", "r:5", "p:4", "l:2", "g:3", "u:1", ",:1", "W:1", "b:1"]
*/