Count Common Words With One Occurrence.js

// Runtime: 141 ms (Top 32.57%) | Memory: 46 MB (Top 62.84%)
var countWords = function(words1, words2) {
    const map1 = new Map();
    const map2 = new Map();
    let count = 0;

    for (const word of words1) {
        map1.set(word, map1.get(word) + 1 || 1);
    }
    for (const word of words2) {
        map2.set(word, map2.get(word) + 1 || 1);
    }
    for (const word of words1) {
        if (map1.get(word) === 1 && map2.get(word) === 1) count++;
    }

    return count;
};