如何让一个函数 return 成为一个 promise

Question

我想return downloadURL调用这个函数的时候，是一个firebase上传函数。

import { storage } from "./base";
import firebase from "firebase";

function uploadFile(file, metadata) {
  return new Promise((resolve, reject) => {
    const task = storage.child(`/${file.name}`).put(file, metadata);

    task.on(
      firebase.storage.TaskEvent.STATE_CHANGED,
      function(snapshot) {
        var progress = (snapshot.bytesTransferred / snapshot.totalBytes) * 100;
        console.log(progress);
      },
      function(error) {
        switch (error.code) {
          case "storage/unauthorized":
            break;
          case "storage/canceled":
            break;
          case "storage/unknown":
            break;
          default:
            break;
        }
        reject(error);
      },
      function() {
        task.snapshot.ref.getDownloadURL().then(function(downloadURL) {
            resolve(downloadURL);
          console.log(downloadURL);
        });
      },
    );
  });
}

export { uploadFile };

我试过了，return downloadURL

Answer 1

您可以简单地尝试如下：

在需要的地方导入文件。
然后用相关参数调用函数。
在 promises 中使用 then 方法来获得解析 downloadUrl

uploddFile(file, data).then(downloadUrl => console.log(downloadUrl) );

Answer 2

试试这个。

         import { storage } from "./base";
         import firebase from "firebase";

         function uploadFile(file, metadata) {
          return new Promise((resolve, reject) => {
          const task = storage.child(`/${file.name}`).put(file, metadata);

          task.on(
           firebase.storage.TaskEvent.STATE_CHANGED,
            function(snapshot) {
             var progress = (snapshot.bytesTransferred / snapshot.totalBytes) * 100;
        console.log(progress);
      },
      function(error) {
        switch (error.code) {
          case "storage/unauthorized":
            break;
          case "storage/canceled":
            break;
          case "storage/unknown":
            break;
          default:
            break;
        }
        reject(error);
      },
        task.snapshot.ref.getDownloadURL().then(function(downloadURL) {
            resolve(downloadURL);
          console.log(downloadURL);
        });
      ,
    );
  });
}

想法是在 getDownloadURL 成功后包含 resolve 方法。然后可以按照上面的答案

中提到的调用来检索

     uploadFile(file, metaData)
     .then((download) => console.log(downloadURL)) ; // Or whatever you want to do wth downloadURL

如何让一个函数 return 成为一个 promise

How to make a function return a promise

javascript

function

promise

es6-promise