javascript - StartsWith() 不能与 takeWhile() 一起使用

Question

我正在尝试迭代不可变列表并让它返回一个新列表，其中包含以特定字符串开头的任何条目。对于此处的示例，我只是试图查找以字母“D”开头的所有州，我希望下面的代码返回一个大小为 1 且“Delaware”作为条目的列表，但它返回带有一个空列表。

const states = Immutable.fromJS([
    "Alabama",
    "Alaska",
    "Arizona",
    "Arkansas",
    "California",
    "Colorado",
    "Connecticut",
    "Delaware"]);
    
function filter() {
  const testA = 'A';
  const filteredOptions = states.takeWhile((option) =>  option.startsWith(testA));
  console.error(filteredOptions.size); // is 4 as I would expect
  
  const testD = 'D';
  const filteredOptions2 = states.takeWhile((option) =>  option.startsWith(testD));
  console.error(filteredOptions2.size); // is 0 when I expect 1
};

filter();

<script src="https://cdnjs.cloudflare.com/ajax/libs/immutable/3.8.2/immutable.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.6.3/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.3/umd/react-dom.production.min.js"></script>

Answer 1

计算机的思维:

Does Alamaba start with A? Yes; I'll take it and continue. Does Alaska start with A? Yes; I'll take it and continue. Does Arizona start with A? Yes; I'll take it and continue. Does Arkansas start with A? Yes; I'll take it and continue. Does California start with A? No, so I stop.

Does Alabama start with D? No, so I stop.

您需要filter，而不是takeWhile。 filter 将获取满足命题的所有元素； takeWhile 仅限序列开头的那些。