可迭代对象和迭代器的示例

数组、字符串和Map的可迭代对象和迭代器

数组的可迭代对象和迭代器

const myArray = [1, 2, 3];

// 使用for...of语句遍历数组
for (let element of myArray) {
  console.log(element);
}

// 手动迭代器遍历数组
const myIterator = myArray[Symbol.iterator]();
console.log(myIterator.next()); // { value: 1, done: false }
console.log(myIterator.next()); // { value: 2, done: false }
console.log(myIterator.next()); // { value: 3, done: false }
console.log(myIterator.next()); // { value: undefined, done: true }

字符串的可迭代对象和迭代器

const myString = 'Hello';

// 使用for...of语句遍历字符串
for (let char of myString) {
  console.log(char);
}

// 手动迭代器遍历字符串
const myIterator = myString[Symbol.iterator]();
console.log(myIterator.next()); // { value: "H", done: false }
console.log(myIterator.next()); // { value: "e", done: false }
console.log(myIterator.next()); // { value: "l", done: false }
console.log(myIterator.next()); // { value: "l", done: false }
console.log(myIterator.next()); // { value: "o", done: false }
console.log(myIterator.next()); // { value: undefined, done: true }

Map的可迭代对象和迭代器

const myMap = new Map([
  ['key1', 'value1'],
  ['key2', 'value2'],
  ['key3', 'value3']
]);

// 使用for...of语句遍历Map
for (let [key, value] of myMap) {
  console.log(key, value);
}

// 手动迭代器遍历Map
const myIterator = myMap[Symbol.iterator]();
console.log(myIterator.next()); // { value: [ "key1", "value1" ], done: false }
console.log(myIterator.next()); // { value: [ "key2", "value2" ], done: false }
console.log(myIterator.next()); // { value: [ "key3", "value3" ], done: false }
console.log(myIterator.next()); // { value: undefined, done: true }

自定义可迭代对象和迭代器的实现

const myIterable = {
  data: ['apple', 'banana', 'orange'],
  [Symbol.iterator]: function() {
    let index = 0;
    const data = this.data;
    return {
      next: function() {
        if (index < data.length) {
          return { value: data[index++], done: false };
        } else {
          return { done: true };
        }
      }
    }
  }
};

// 使用for...of语句遍历自定义可迭代对象
for (let fruit of myIterable) {
  console.log(fruit);
}

// 手动迭代器遍历自定义可迭代对象
const myIterator = myIterable[Symbol.iterator]();
console.log(myIterator.next()); // { value: "apple", done: false }
console.log(myIterator.next()); // { value: "banana", done: false }
console.log(myIterator.next()); // { value: "orange", done: false }
console.log(myIterator.next()); // { done: true }

使用可迭代对象和迭代器进行编程的示例

示例1: 生成一个可迭代对象，该可迭代对象的迭代器可以生成一个等差数列

function makeRangeIterator(start = 0, end = Infinity, step = 1) {
  let nextIndex = start;
  let iterationCount = 0;

  const rangeIterator = {
    next: function() {
      let result;
      if (nextIndex < end) {
        result = { value: nextIndex, done: false };
        nextIndex += step;
        iterationCount++;
        return result;
      }
      return { value: iterationCount, done: true };
    }
  };
  return rangeIterator;
}

示例2: 计算数组中所有数字的平均值

function average(...nums) {
  const iterator = nums[Symbol.iterator]();
  let sum = 0;
  let count = 0;
  let result = iterator.next();
  while (!result.done) {
    sum += result.value;
    count++;
    result = iterator.next();
  }
  return sum / count;
}

示例3: 从字符串中找到第一个元音字母

function findFirstVowel(str) {
  const iterator = str[Symbol.iterator]();
  let result = iterator.next();
  while (!result.done) {
    if (isVowel(result.value)) {
      return result.value;
    }
    result = iterator.next();
  }
  return undefined;
}

function isVowel(char) {
  return ['a', 'e', 'i', 'o', 'u'].includes(char.toLowerCase());
}