问使用WebExtensions API操作下载的文件

EN

var ignoreDownloadUrls=[];
var ignoreDownloadIds=[];

chrome.downloads.onCreated.addlistener(forceDownloadFilenameIfUrlMatch);

function forceDownloadFilenameIfUrlMatch(downloadItem){
    //Check the URL for duplication (may not be needed, need to test).
    let foundUrlIndex = ignoreDownloadUrls.findIndex(function(element,index){
        if(element === downloadItem.url){
            return true;
        }//else
        return false;
    });
    if(foundUrlIndex>-1) {
        //This is the callback resulting from our creating the download
        //  with the new filename. We only want to ignore the URL once,
        //  so, remove the URL from our ignore list.
        //  This makes the assumption that the events we get are reasonably
        //  orderly (only one created event per URL which we want to
        //  change, etc.). This may need to be more complex in real use.
        ignoreDownloadUrls.splice(foundUrlIndex,1);
        //We do not want to change this download, as we created it.
        return;
    }
    //Test the ID for one we created:
    let foundIdIndex = ignoreDownloadIds.findIndex(function(element,index){
        if(element === downloadItem.id){
            return true;
        }//else
        return false;
    });
    if(foundIdIndex>-1) {
        //This is an event resulting from our creating the download
        //  with the new filename.
        //We do not want to change this download, as we created it.
        return;
    }
    if(downloadItem.url.idexOf(myMatchString) >-1){
        chrome.downloads.cancel(downloadItem.id);
        //Remember the URL so we don't change it twice.
        //  Remembering the URL may not be the best way to do this. Need
        //  to test as to the order which events and the download callback
        //  occur.
        ignoreDownloadUrls.push(download.url);
        chrome.downloads.download({
            url: downloadItem.url,
            filename: myNewFilename
        }, function(id){
        //We could use the callback of the downloads.download() to remember
        //  the downloadId of the download we created and only ignore that
        //  one.  That would rely on the callback being called prior to the
        //  new onCreated event. Might work that way in practice. It
        //  would certainly be better to remember the specifically created
        //  downloadId rather than just ignore (once) a specific URL.
        //  Testing should indicate if we need to use the download ID,
        //  or ignore the URL (once).
            //Remember the downloadId so we don't change it twice.
            ignoreDownloadIds.push(id);
        });
    }
}