Question

按照此处的文档：https://developer.mozilla.org/en-US/Add-ons/WebExtensions/API/downloads/download

var options = {
  filename: 'dummyName.txt',
  url: 'https://some.url',
  conflictAction: 'uniquify',
  saveAs: true
};
var downloading = browser.downloads.download(options, function() {
  console.log('In callback');
});

console.log(downloading);
downloading.then(function() {
  console.log('started');
}, function() {
  console.log('failed');
});

在控制台中，我看到..

undefined
downloading is undefined
In callback
Unchecked lastError value: Error: Download canceled by the user

如果用户取消了对话框保存，如何阻止downloading.then内的代码运行？

Answer 1

实际上很简单。只需从下载功能中删除function（）部分，如下所示：

var options = {
    filename: 'dummyName.txt',
    url: 'https://some.url',
    conflictAction: 'uniquify',
    saveAs: true
};
var downloading = browser.downloads.download(options);

console.log("downloading object is " + downloading);

downloading.then(function(id) {
    console.log('started' + id);
}, function(error) {
    if(error.message == "Download canceled by the user"){
        // Do something
        console.log("not going into the success callback..");
    }else{
        console.log('failed' + error);
    }
});

您混合了回调语法（您在下载调用中包含的函数（））和基于Promise的语法（然后是（））。

如果您想要正确捕获错误，最好使用基于Promise的语法来开发Firefox插件。

请注意，您可以简化此

var downloading = browser.downloads.download(options);
downloading.then(onSuccess, onError);

到

browser.downloads.download(options).then(onSuccess, onError);

开发Firefox插件祝你好运！

在saveAs对话框取消时检测

1 个答案: