javascript - 无法在回调函数中调用任何 fineUploader 方法

Question

我将 autoUpload 设置为 false，因为我想自己将图像上传到我的后端。但是，为此我首先需要文件对象。在回调 onSubmitted 事件中，我试图将图像 ID 传递给 getFile 方法，以返回对象。但是，当我尝试这样做时，我收到以下错误消息。

in onSubmitted: id=0 | name=28603454_15219061700_r.jpg index.js:2178

[Fine Uploader 5.16.2] Caught exception in 'onSubmitted' callback - Cannot read property 'uploader' of null

我猜我得到这个是因为我正在声明一个 const 对象并同时引用它，我相信你不能这样做......

那么，关于如何在 callbacks 函数中调用方法有什么想法吗？或者还有其他方法吗？

const uploader = new FineUploaderTraditional({
  options: {
    maxConnections: 1,
    autoUpload: false,
    deleteFile: { enabled: true, endpoint: "/uploads" },
    request: { endpoint: "/uploads" },
    retry: { enableAuto: true },
    callbacks: {
      onSubmitted: function(id, name) {
        console.log("in onSubmitted: id=" + id + " | name=" + name);
        // getFile(id) returns a `File` or `Blob` object.
        console.log(this.uploader.getFile(id));
      }
    }
  }
});

更新我现在已经获取了我所有的精细 uploader 代码并用它创建了一个新组件。我仍然面临同样的问题。组件代码如下:

FineUploader.jsx

import React, { Component } from "react";
import FineUploaderTraditional from "fine-uploader-wrappers";
import Gallery from "react-fine-uploader";
import Filename from "react-fine-uploader/filename";
import "react-fine-uploader/gallery/gallery.css";

const util = require("util");

const uploader = new FineUploaderTraditional({
  options: {
    // debug: true,
    maxConnections: 1,
    autoUpload: false,
    deleteFile: { enabled: true, endpoint: "/uploads" },
    request: { endpoint: "/uploads" },
    retry: { enableAuto: true },
    validation: {
      acceptFiles: ".jpg,.png,.gif,.jpeg",
      allowedExtensions: ["jpg", "png", "gif", "jpeg"],
      itemLimit: 5,
      sizeLimit: 5000000
    },
    callbacks: {
      onCancel: function() {
        console.log("in onCancel: ");
      },
      onComplete: function(id, name, responseJSON, xhr) {
        console.log("in onComplete: " + id + " | " + name + " | " + responseJSON + " | " + xhr);
      },
      onAllComplete: function(succeeded, failed) {
        console.log("in onAllComplete: " + succeeded + " | " + failed);
      },
      onProgress: function(id, name, uploadedBytes, totalBytes) {
        console.log("in onProgress: " + id + " | " + name + " | " + uploadedBytes + " | " + totalBytes);
      },
      onError: function(id, name, errorReason, xhr) {
        console.log("in onError: " + id + " | " + name + " | " + errorReason + " | " + xhr);
      },
      onDelete: function(id) {
        console.log("in onDelete: " + id);
      },
      onDeleteComplete: function(id, xhr, isError) {
        console.log("in onDeleteComplete: " + id + " | " + xhr + " | " + isError);
      },
      onPasteReceived: function(blob) {
        console.log("in onPasteReceived: " + blob);
      },
      onResume: function(id, name, chunkData, customResumeData) {
        console.log("in onResume: " + id + " | " + name + " | " + chunkData + " | " + customResumeData);
      },
      onStatusChange: function(id, oldStatus, newStatus) {
        console.log("in onStatusChange: " + id + " | " + oldStatus + " | " + newStatus);
      },
      onSubmit: function(id, name) {
        console.log("in onSubmit: " + id + " | " + name);
      },
      onSubmitted: function(id, name) {
        console.log("in onSubmitted: id=" + id + " | name=" + name);
        // getFile(id) returns a `File` or `Blob` object.
        // console.log(this.uploader.getFile(id));
        // console.log(uploader.getFile(id));
        // nothing here is working.... :(
      },
      onUpload: function(id, name) {
        console.log("in onUpload: " + id + " | " + name);
      },
      onValidate: function(data, buttonContainer) {
        console.log(
          "in onValidate: " + util.inspect(data, { showHidden: true, depth: null }) + " | " + buttonContainer
        );
      },
      onSessionRequestComplete: function(response, success, xhrOrXdr) {
        console.log("in onSessionRequestComplete: " + response + " | " + success + " | " + xhrOrXdr);
      }
    }
  }
});

const fileInputChildren = <span>Click to Add Photos</span>;
const statusTextOverride = {
  upload_successful: "Success!"
};

class FineUploader extends Component {
  constructor() {
    super();

    this.state = {
      submittedFiles: []
    };
  }

  componentDidMount() {
    uploader.on("submitted", id => {
      const submittedFiles = this.state.submittedFiles;
      console.log("submittedFiles: " + submittedFiles);

      submittedFiles.push(id);
      this.setState({ submittedFiles });
    });
  }

  render() {
    return (
      <div>
        {this.state.submittedFiles.map(id => (
          <Filename id={id} uploader={uploader} />
        ))}
        <Gallery
          fileInput-children={fileInputChildren}
          status-text={{ text: statusTextOverride }}
          uploader={uploader}
        />
      </div>
    );
  }
}

export default FineUploader;

并且 -- 现在在主页上，我正在导入 FineUploader.jsx，并使用该组件。

import FineUploader from "../../components/FineUploader";

在我的渲染方法中我有:

<FineUploader />

Answer 1

this 在 javascript 中很棘手。在常规函数(例如，function f(){...})中，this 取决于函数在哪里被调用，而不是它在哪里被定义为。通过第 3 方 API 使用回调时，您实际上无法控制它的调用位置，因此您最终可能会遇到上述错误。

幸运的是，您可以使用箭头函数(例如，const f = () => {...};)根据函数所在的位置绑定(bind) this 定义。

参见 MDN docs了解更多信息，或者您可以引用 this excellent SO answer .

但是，特别是对于您的代码，当您定义 onSubmitted 只是全局/窗口对象时，我不确定其中任何一个都可以作为您的 this 。

为了让它工作，您需要在顶层创建一个闭包(就在您实际创建 uploader 之前):

function onSubmitted(id, name) {
    console.log("in onSubmitted: id=" + id + " | name=" + name);
    // getFile(id) returns a `File` or `Blob` object.
    console.log(uploader.getFile(id));
}

const uploader = new FineUploaderTraditional({..., callbacks: {onSubmitted, ...}});

这将允许您在实际实例化 uploader 之前定义与 uploader 交互的逻辑(这就是您想要的样子)。请注意缺少 this，因为我们只是利用 js 闭包规则。