count = function(arr, item) {

    return arr.filter(function(x){return x==item}).length

}

​

count([1,2,3,2,4,2], 2);

count = function(arr, item) {

    var count = 0;

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

        if(arr[i] == item)

            count++;

    }

    return count

}

​

count([1,2,3,2,4,2], 2);

count = function(arr, item) {

    return arr.reduce(function(total,x){return x==item ? total+1 : total}, 0);

}

​

count([1,2,3,2,4,2], 2);

count = function(arr, item) {

    var regex = new RegExp('[^'+item+']+', 'g');

    return String(arr).replace(regex,'').length

}

​

count([1,2,3,2,4,2], 3);

count = function(arr, item) {

    var count= 0, i;

    while((i= arr.indexOf(item, i))!= -1){

        ++count;

        ++i;

    }   

    return count;

}

​

count([1,2,3,2,4,2], 2);