JavaScript 如何查找一篇英文文章中出现频率最高的单词？

function findMostWord(article) {

// 合法性判断
if (!article) return;

// 参数处理
article = article.trim().toLowerCase();

let wordList = article.match(/[a-z]+/g),
  visited = [],
  maxNum = 0,
  maxWord = "";

article = " " + wordList.join("  ") + " ";

// 遍历判断单词出现次数
wordList.forEach(function (item) {
  if (visited.indexOf(item) < 0) {
    let word = new RegExp(" " + item + " ", "g"),
      num = article.match(word).length;

    if (num > maxNum) {
      maxNum = num;
      maxWord = item;
    }
  }
});

return maxWord + "  " + maxNum;

}