javascript - 函数返回未定义的、预期的 Promise 或值，而我返回新的 Promise

Question

为什么我收到“函数返回未定义，预期的 promise 或值”？我无法理解。也许我错过了一些东西。

function getImage(url) {
  console.log('Begin get image');
  return new Promise(function(resolve, reject) {
  https.get(url, res => {
    // Initialise an array
    const bufs = [];

    // Add the data to the buffer collection
    res.on('data', function (chunk) {
      console.log('on data image');
      bufs.push(chunk)
    });

    // This signifies the end of a request
    res.on('end', function () {
      console.log('on end image');

      // We can join all of the 'chunks' of the image together
      const data = Buffer.concat(bufs);

      resolve(data);
    });
  })
    // Inform the callback of the error.
    .on('error', function (error) {
      reject(error);
    });
});
}

这是我调用该函数的地方:

getImage(imageURL)
      .then( dataImg => {
        console.log('image get get');
        (...)
      }

我应该获取 dataImg 并进行操作。

Answer 1

我使用 Node 测试了以下代码并收到了图像缓冲区。也许检查一下您是否在某处遗漏了一些括号。

var https = require("https");

function getImage(url) {
    console.log('Begin get image');

    // Return the loading-promise
    return (new Promise((resolve, reject) => {
        https.get(url, (res) => {
                // Initialise an array to store the image-data
                const bufs = [];

                // Add the data to the buffer collection
                res.on('data', function(chunk) {
                    console.log('on data image');
                    // Push the recieved chunks into the array
                    bufs.push(chunk)
                });

                // This signifies the end of a request
                res.on('end', function() {
                    console.log('on end image');

                    // We can join all of the 'chunks' of the image together
                    const data = Buffer.concat(bufs);

                    // Return the image-buffer
                    resolve(data);
                });
            })
            // Inform the callback of the error.
            .on('error', function(error) {
                reject(error);
            });
    }));
}

(function() {
    getImage("https://preview.redd.it/utrlx02sx2431.jpg?width=640&crop=smart&auto=webp&s=8ed20013607e0d6019f59ab01b0e4930eb913351")
        .then((dataImg) => {
            console.log('image get get');
            console.log(dataImg);
        });
})();

控制台输出:

ab@xy:~/test$ node testrun.js 
Begin get image
on data image
on data image
on end image
image get get
<Buffer ff d8 ff e0 00 10 4a 46 49 46 00 01 01 01 00 00 00 00 00 00 ff e1 00 42 45 78 69 66 00 00 4d 4d 00 2a 00 00 00 08 00 01 87 69 00 04 00 00 00 01 00 00 ... 20311 more bytes>