SOURCE

function repeat_word(str) {
  let strArr = str.split(' ');
  console.log('原始数组:' + strArr  + ' 长度:' + strArr.length);

  let tally = {}; //统计
  for (let i = 0; i < strArr.length; i++) {//遍历所有的word
    let word = strArr[i];

    if (tally[word]) { //判断是否存在
      tally[word] += 1;
    } else {
      tally[word] = 1;
    }
  }
  for (let word in tally) {
    if (tally[word] > 1) {
    	console.log(word);
    }
  };
}

// let str = prompt('输入') || '';
let str = 'abc abc dsfs fdsf';
repeat_word(str);