Page-level JavaScript function to return the number of occurrences in an array of values

countIf.js

/**
 * Return the number of occurrences in a list
 * @param  {Array}            arr   list of primitive values (string, numeric, boolean)
 * @param  {String|Numeric}   x     the value to be searched for
 * @return {Int}                    the count of occurrences
 */
function countIf(arr,x) {
   var count = 0;
   if(arr && Array.isArray(arr)) {
      for(var i=0; i<arr.length; i++) {
         if(arr[i] == x) count++;
      }
   }
   return count;
}