constructing more complex for-loops

Question

How to put the k var in the for-loop construction. I want more compact code, not like this one:

var k = 0;
for (var i = 0; i < arr.length; i++) {
   if (arr[i] == 'x') {
       k++;
   }
}

Answer 1

Although not as efficient due to the fact that a new array is constructed, using filter leads to far more compact code.

arr.filter(function(e){ return e == 'x'; }).length;

An alternative, although far less clear avoids constructing a new array:

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