理解Javascript回调参数 [英] Understanding Javascript callback parameters

问题描述

关于回调的几个问题，使用一些示例代码..

A few questions on callbacks, using some example code..

function uploadPhoto(params){

    var win = function(response){
       console.log("Success!");
       console.log("Response: ", response); 
    }

    var fail = function(error){
      console.log("Failed.");
      console.log("Error: ", error);
    }

    var options = {params: params};
    var ft = new FileTransfer();
    ft.upload(params.img_uri, "localhost:3000/testing"), win, fail, options);
}

在上面的例子中，我们可以使用FileTransfer将图像上传到服务器。如果成功，它将调用 win 函数，如果不成功，则调用 fail 函数。

In the above example, using FileTransfer we can upload an image to a server. If successful, it will call the win function, and if not successful, call the fail function.

获胜和失败函数如何接收 回复或错误参数？我们没有调用 win（响应）或失败（错误），那么javascript如何在没有我们的情况下接受这些参数在我们的 ft.upload（）行设置它们？

How do the win and fail functions receive the response or error parameters? We're not calling win(response) or fail(error), so how does javascript accept these parameters without us setting them on our ft.upload() line?

更多示例代码：

function win(response){
  console.log("Success!");
  console.log(response);
};

function fail(error){
  console.log("Failed.");
  console.log("Error: ", error);
};

function uploadPhoto(params){
  var options = {params: params};
  var ft = new FileTransfer();
  ft.upload(params.img_uri, "localhost:3000/testing"), win, fail, options);
};

在第二个例子中，我发现 win 函数，但是它的'response'参数未定义。这是什么原因？

In this second example, I've found that the win function can be called, however its 'response' parameter comes up undefined. What is the reason for this?

如果我想让我的 win 函数也接受 params 来自上传功能，所以看起来更像是这样：

What if I wanted to have my win function to also accept params from the upload function, so it would look more like this:

var win = function(response, parameters){
  console.log("Success with parameters: ", parameters);
  console.log("Response: ", response);
}

我的 ft.upload 行需要看起来更像这样：

Would my ft.upload line need to look more like this:

ft.upload(params.img_uri, "localhost:3000/testing", win(null, params), fail, options);

这里有很多小问题，感谢您的帮助！

Lots of little questions here, Thanks for your help!

推荐答案

获胜和失败函数如何接收 响应或错误参数？我们没有调用 win（响应）或失败（错误），那么javascript如何在没有我们的情况下接受这些参数在我们的 ft.upload（）行设置它们？

How do the win and fail functions receive the response or error parameters? We're not calling win(response) or fail(error), so how does javascript accept these parameters without us setting them on our ft.upload() line?

ft.upload 调用 win 或失败并为其提供值回复或错误。也就是说， ft.upload 可能如下所示：

ft.upload calls win or fail and supplies it with a value for response or error. That is, ft.upload might look something like this:

function upload(arg1, arg2, successCallback, failureCallback, options) {
  try {
    var response = something(...);
    successCallback(response);
  } catch(ex) {
    failureCallback(ex);
  }
}

现在，当你致电 ft.upload（params.img_uri，localhost：3000 / testing，win，fail，options）， win 传递给上传作为 successCallback 参数，失败作为 failureCallback 和 upload 依次使用适当的参数调用其中一个。

Now, when you call ft.upload(params.img_uri, "localhost:3000/testing", win, fail, options), win is passed to upload as the successCallback argument and fail as failureCallback, and upload in turn calls one or the other with an appropriate argument.

如果我想让我的 win 函数也从上传中接受 params 该怎么办？函数，所以看起来更像是这样：

What if I wanted to have my win function to also accept params from the upload function, so it would look more like this:

var win = function(response, parameters){
  console.log("Success with parameters: ", parameters);
  console.log("Response: ", response);
}

我的 ft.upload 行需要看起来更像这样：

Would my ft.upload line need to look more like this:

ft.upload(params.img_uri, "localhost:3000/testing"), win(null, params), fail, options);

关闭，但不完全。如果你这样做，你将传递任何 win 和失败作为参数返回，除非它们返回将返回的函数当 ft.upload 试图调用它们时会出现问题。

Close, but not quite. If you do that, you're passing whatever win and fail return as arguments, and unless they return functions that will be a problem when ft.upload tries to call them.

...这不是巧合，是一个解决方案：让它们返回 ft.upload 可以调用的函数：

...which, not coincidentally, is one solution: Make them return functions that ft.upload can call:

function makeSuccessCallback(parameters) {
  return function successCallback(response) {
    console.log("Success with parameters: ", parameters);
    console.log("Response: ", response);
  }
}

var win = makeSuccessCallback(params);
ft.upload(params.img_uri, "localhost:3000/testing", win, fail, options);

另一种选择是使用 Function.prototype.bind 。您可能已经看到 bind 用于设置函数的此对象，但我们也可以将其他参数传递给 bind ，返回的函数将使用这些参数作为自己的初始参数。在计算机科学中，这被称为currying。例如：

The other option is to use Function.prototype.bind. You may have seen bind used to set a function's this object, but we can also pass additional arguments to bind and the returned function will use those arguments as its own, initial arguments. In computer science this is called "currying." For example:

function add(n, m) {
  return n + m;
}

var addThree = add.bind(null, 3);
addThree(4); // => 7

var ten = add.bind(null, 4, 6);
ten(); => 10

（由于此功能不关心此，我们只为第一个参数传递 null 。）

(Since this function doesn't care about this, we just pass null for the first argument.)

使用回调我们可以用它来获取一个函数的副本，但其第一个参数是内置的：

With callbacks we can use this to get a "copy" of a function but with its first argument(s) "built in":

function successCallback(parameters, response) {
  console.log("Success with parameters: ", parameters);
  console.log("Response: ", response);
}

var win = successCallback.bind(null, params);
ft.upload(params.img_uri, "localhost:3000/testing", win, fail, options);

这样，当 ft.upload 来电时 win（响应），它实际上会调用 successCallback（params，response）。

This way, when ft.upload calls win(response), it will actually be calling successCallback(params, response).

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