// http://stackoverflow.com/questions/25602372/counting-unique-words-in-strings/25602535#25602535

​

var seen = {};

​

count(["a", "b"], seen);

count(["a", "c"], seen);

​

function count(words, accumulator) {

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

        if(!accumulator.hasOwnProperty(words[i])) {

          accumulator[words[i]] = 1;

        } else {

          ++accumulator[words[i]];

        }

    }

}

​

​