var arrNumber = [1, 0, 9, 4, 8, 5, 7, 3, 2, 8, 6, 2, 4, 6, 8, 3, 5, 7, 5];

var arrString = ["a", "u", "e", "o", "i", "a", "i", "u", "i"];

var arrDuplicateValues = [];

​

// Count duplicated values

arrDuplicateValues = new Array();

arrNumber.forEach(function(x) {

  arrDuplicateValues[x] = (arrDuplicateValues[x] || 0) + 1;

});

console.log(arrDuplicateValues);

​

arrDuplicateValues = new Array();

arrString.forEach(function(x) {

  arrDuplicateValues[x] = (arrDuplicateValues[x] || 0) + 1;

});

console.log(arrDuplicateValues);

console.log(arrDuplicateValues["i"]);