并发限制图片加载数量

function loadImage
(url
, index
) {
  return new Promise
((resolve
, reject
) => {
    console
.log
(`#${index
} url: ${url
} start`);
    setTimeout
(() => {
      console
.log
(`url: ${url
} ok`);
      resolve
();
    }, 500);
  });
}

function limitLoad
(urls
, handler
, limit
) {
  const sequence
 = [...urls
];
  // 存储异步处理函数的结果
  let promises
 = [];
  // 限流加载前 limit 个 url
  promises
 = sequence
.splice
(0, limit
).map
((url
, index
) => {
    return handler
(url
, index
).then(() => index
);
  });
  // 先执行第一轮，然后循环处理剩余 url
  let p
 = Promise
.race
(promises
);
  for (let i
 = 0; i
 < sequence
.length
; i
++) {
    p
 = p
.then
((data
) => {
      promises
[data
] = handler
(sequence
[i
], i
).then(() => data
);
      return Promise
.race
(promises
);
    });
  }
}

// 加载 10 张图片，并发量为 3
limitLoad
(
  [
    "https://example.com/article-1",
    "https://example.org/gallery/image-2.jpg",
    "https://samplewebsite.net/blog/post-3",
    "https://anotherwebpage.com/videos/watch?v=video-4",
    "https://api.example.io/data/v1/resource-5",
    "https://www.example-edu.com/courses/course-6",
    "https://news-sites.com/top-stories/story-7",
    "https://e-commerce-site.com/products/product-8",
    "https://docs.example-help.com/guides/guide-9",
    "https://social-media-platform.com/profile/user-10",
  ],
  loadImage
,
  3
);
并发限制图片加载数量 ​

并发限制图片加载数量
