使链表在ES6中可迭代

Question

我在JavaScript中有一个链表，我需要用for of循环使其可迭代。我几乎已经完成了，但似乎没有办法将第一个值包含在结果中。这是一个简化的版本：

var obj = {value: 1, next: {value: 2, next: {value: 3, next: {value: 4, next: {value: 5, next: {value: 6, next: {value:7, next: null}}}}}}};

obj[Symbol.iterator] = function() {
  var current = this;
  return {
    next() {
      if (current.next !== null) {
        current = current.next;
        return {value: current.value, done: false};
      }
      return {done: true}
    }
  }
}

for (const x of obj) {
  console.log(x)
}

// this is how you get the values printed with no loop
// console.log(obj.value + '->' + obj.next.value + '->' + obj.next.next.value)

Answer 1

问题是在检索value之前，您要将current移动到下一个节点。

​

var obj = {value: 1, next: {value: 2, next: {value: 3, next: {value: 4, next: {value: 5, next: {value: 6, next: {value:7, next: null}}}}}}};

obj[Symbol.iterator] = function() {
  var current = this;
  return {
    next() {
      if (current) {
        var value = current.value;
        current = current.next;
        return {value: value, done: false};
      }
      return {done: true};
    }
  };
};

for (const x of obj) {
  console.log(x);
}

​

使用generator function实现迭代器要容易得多。

​

var obj = {value: 1, next: {value: 2, next: {value: 3, next: {value: 4, next: {value: 5, next: {value: 6, next: {value:7, next: null}}}}}}};

obj[Symbol.iterator] = function*() {
  var current = this;
  while (current) {
    yield current.value;
    current = current.next;
  }
};

for (const x of obj) {
  console.log(x);
}

​

Answer 2

您应该测试current，而不是current.next

obj[Symbol.iterator] = function() {
  var current = this;
  return {
    next() {
      if (current !== null) {
        var res = {value: current.value, done: false};
        current = current.next;
        return res;
      } else {
        return {done: true};
      }
    }
  };
}

但可以将其作为生成器方法编写得更简单：

obj[Symbol.iterator] = function* () {
  for (var current = this; current !== null; current = current.next) {
    yield current.value;
  }
}

顺便说一句，我建议不要把这个迭代器放在列表的每个节点上(甚至在第一个节点上)。放入一个指向列表头部的单独对象，或使其成为一个静态辅助函数：

let list = {
  head: obj, // could be null either
  *[Symbol.iterator]() {
    for (var current = this.head; current !== null; current = current.next) {
      yield current.value;
    }
  }
}

​

function* linkedList(head)
  for (; head !== null; head = head.next) {
    yield head.value;
  } 
}