下载前获取放置在远程服务器上的图片大小

function getImageSize(url) {
  return new Promise((resolve, reject) => {
    const xhr = new XMLHttpRequest();
    xhr.open('HEAD', url);
    xhr.onreadystatechange = function() {
      if (xhr.readyState === 4) {
        if (xhr.status === 200) {
          const contentLength = xhr.getResponseHeader('Content-Length');
          resolve(parseInt(contentLength));
        } else {
          reject(new Error('Failed to fetch image size'));
        }
      }
    };
    xhr.send();
  });
}

const imageUrl = 'https://example.com/image.jpg';
getImageSize(imageUrl)
  .then(size => {
    console.log('Image size:', size);
    // 进行后续操作
  })
  .catch(error => {
    console.error(error);
  });

const http = require('http');

function getImageSize(url) {
  return new Promise((resolve, reject) => {
    http
      .request(url, { method: 'HEAD' }, response => {
        if (response.statusCode === 200) {
          const contentLength = response.headers['content-length'];
          resolve(parseInt(contentLength));
        } else {
          reject(new Error('Failed to fetch image size'));
        }
      })
      .on('error', error => {
        reject(error);
      })
      .end();
  });
}

const imageUrl = 'https://example.com/image.jpg';
getImageSize(imageUrl)
  .then(size => {
    console.log('Image size:', size);
    // 进行后续操作
  })
  .catch(error => {
    console.error(error);
  });