如何同步从Google云端硬盘下载文件？

Question

还是有办法产生相同的效果，即JavaScript程序停止直到下载完成（不使用setTimeout ）？

Answer 1

Javascript is asynchronous, so you need to handle the download asynchronously. This is mainly because javascript runs single threaded and that's generally shared with the UI thread, so if you blocked your code on a download the user wouldn't be able to interact with the page at all until your code finished.

However, handling it asynchronously shouldn't be difficult, so long as the mechanism you're using to download the file supports a callback when it's done (which most should).

Say you had the following code:

function doDownload(url) {
  doSomeInitialStuff();
  startDownload(url);  // assuming this would block, which it can't
  doSomeOtherStuff();
  doMoreOtherStuff();
}

If your download mechanism supports a callback when it's done (a function that's called after the download is complete or has failed), then you would restructure your code like so:

function doDownload(url) {
  doSomeInitialStuff();
  startDownload(url, onDownloadComplete);
}

function onDownloadComplete() {
  doSomeOtherStuff();
  doMoreOtherStuff();
}

The specifics of how you callback works (args passed to it, how it's provided to the download code) will vary depending on the js libraries you're using, but this is the basic idea for how to handle it asynchronously.