javascript - Javascript 中 reduce 方法的奇怪行为

Question

谁能给我解释一下这种情况？

第二次调用该函数，结果为{cat: 2, cat,cat: 1, dog: 1, frog: 1}。

但是，我认为结果会是 {cat: 4, dog: 1, frog: 1}。

这是怎么回事？

var animals = ['cat', 'cat', ['cat'], 'dog', 'frog'];

var otherAnimals = ['cat', 'cat', ['cat', 'cat'], 'dog', 'frog'];

function reducingArrays(arraySource) {
  var countedData = arraySource.reduce(function(allItems, item) {
    if (item in allItems) {
      allItems[item]++;
    } else {
      allItems[item] = 1;
    }
    return allItems;
  }, {});

  console.log(countedData);
}

reducingArrays(animals); // {cat: 3, dog: 1, frog: 1}

reducingArrays(otherAnimals); // {cat: 2, cat,cat: 1, dog: 1, frog: 1}
// What I expected: {cat: 4, dog: 1, frog: 1}

Answer 1

您可以将单个元素转换为数组:

var animals = ['cat', 'cat', ['cat'], 'dog', 'frog'];

var otherAnimals = ['cat', 'cat', ['cat', 'cat'], 'dog', 'frog'];

function reducingArrays(arraySource) {
  var countedData = arraySource.reduce(function(allItems, item) {
    var arr = Array.isArray(item) ? item : [item];
    allItems[arr[0]] = (allItems[arr[0]] || 0) + arr.length;
    return allItems;
  }, {});

  console.log(countedData);
}

reducingArrays(animals);

reducingArrays(otherAnimals);