Question

我正在使用firebase并注意到大多数方法都在返回promise，但在文档中这个不是。是否有可能将此变为承诺？

uploadTask.on(
    'state_changed',
    function(snapshot) {
        const progress = snapshot.bytesTransferred / snapshot.totalBytes * 100;
        console.log('Upload is ' + progress + '% done');
    },
    function(error) {
        alert(error);
    },
    function() {
        const downloadURL = uploadTask.snapshot.downloadURL;
        console.log(downloadURL);
    }
);

Answer 1

如果您希望在上传完成时解决某些承诺，请使用此通用模式：

const promise = new Promise((resolve, reject) => {
    // whenever the work is complete and successful
    resolve()
    // or, whenever the work finishes with an error
    reject()
})

According to the API docs，对于适用于Firebase UploadTask的云端存储，您的on处理程序将收到＆＃34;完成＆＃34;的回调作为您的第四个参数。所以你可以像这样修改它：

const promise = new Promise((resolve, reject) => {
   uploadTask.on(
    'state_changed',
    function(snapshot) {
      const progress = snapshot.bytesTransferred / snapshot.totalBytes * 100;
      console.log('Upload is ' + progress + '% done');
    },
    function(error) {
      reject(error);  // added this line
      alert(error);
    },
    function() {
      const downloadURL = uploadTask.snapshot.downloadURL;
      console.log(downloadURL);
      resolve();  // added this line
    }
  );
});

您可以看到我在您的代码中添加了对resolve和reject的调用，现在已嵌入到Promise中的闭包中。

是否可以将firebase的图像上传“uploadTask.on”监听器转换为承诺？

1 个答案: