将变量绑定到回调函数 [英] Bind variables to callback function

问题描述

我的控制器中有一些函数调用了一些数据库函数。所有这些数据库函数都执行错误回调，这意味着如果发生数据库错误，它们会执行单独的回调来处理错误。示例：

I have a few functions in my controller which call some database functions. All of these database functions do "error callbacks", meaning that if a database error occur they do a separate callback which handles the error. Example:

exports.referralComplete = function(req, res){
    /*getting id etc.*/
    db.startDatabaseConnection(function() {
        db.flagReferralAsDone(id, function(success) {
            db.endDatabaseConnection();
            /*doing stuff on success*/
        }, onError);
    }, onError);

    function onError(err, description) {
        logger.error(description + ": " + err);
        user.pageNotFound(req, res);
    }
}

我有多个与此类似的函数，它们正在调用不同的数据库功能问题是我现在已经将onError（）复制到每个的范围内，因为我在处理错误时需要req和res变量。我当然可以将res和req传递给数据库函数，然后将它们作为参数传递给错误回调，但我觉得可能有更好的方法。

I have multiple functions similar to this, which are calling different database functions. The problem is that I at the moment have duplicated onError() into the scope of each of them, since I need the req and res variables when handling the error. I could of course pass res and req to the database function, and then pass them as arguments to the error callback, but I like think that there might be a better way.

所以问题是：是否有可能以某种方式将res和req绑定到全局onError回调函数，以某种方式我不必将变量作为参数传递给db函数？

So the question is: Is it possible to somehow bind res and req to a global onError callback function, in a way that I won't have to pass the variables as arguments to the db function?

我对node.js和javascript很新，所以如果有更好的方法来处理错误，请告诉我。

I'm very new to node.js and javascript in general, so if there is a better way of handling errors, please let me know.

推荐答案

绑定很简单！

db.startDatabaseConnection(function(){
  // whatever
}, onError.bind(this, var1, var2));

您可以通过点击这个很棒的链接来了解有关绑定的更多信息，即使该链接有点长。

这是一个真正的基本演示

Here's a real basic demo

// a function
var something = function (a, b, c) {
  console.log(a, b, c);
};

// a binding of something with 3 defined args
var b = something.bind(null, 1, 2, 3);

// call b
b();
//=> 1 2 3

在幕后，这基本上就是发生了什么

Behind the scenes, this is basically what's happening

// ES6
const myBind = (f, context, ...x) =>
  (...y) => f.call(context, ...x, ...y);

// ES5
var myBind = function(fn, context) {
  var x = Array.prototype.slice.call(arguments, 2);
  return function() {
    var y = Array.prototype.slice.call(arguments, 0); 
    return fn.apply(context, x.concat(y));
  };
};

var b = myBind(console.log, console, 1, 2, 3);

b();
// => 1 2 3

b(4,5,6)
// => 1 2 3 4 5 6 

---

部分应用程序

类似于 bind ing是部分申请

在计算机科学中，部分申请（或部分申请）函数应用程序）指的是修复一个函数的多个参数的过程，产生另一个较小的arity函数。

In computer science, partial application (or partial function application) refers to the process of fixing a number of arguments to a function, producing another function of smaller arity.

我们可以制作一个非常简单的部分帮助程序，帮助我们完成这个

Here we could make a very simple partial helper procedure which helps us accomplish this

const identity = x =>
  x

const partial = (f = identity, ...x) =>
  (...y) => f (...x, ...y)

const foo = (...all) =>
  console.log ('array of', all)

partial (foo, 1, 2, 3) (4, 5, 6)
// 'array of', [ 1, 2, 3, 4, 5, 6 ]

Currying

Currying 是与约束或部分应用相关但不相同

Currying is related to, but not the same as, binding or partial application

在数学和计算机科学中，currying是翻译评估的技巧一个函数，它接受多个参数（或一个参数元组）来评估一系列函数，每个函数都有一个参数。

In mathematics and computer science, currying is the technique of translating the evaluation of a function that takes multiple arguments (or a tuple of arguments) into evaluating a sequence of functions, each with a single argument.

const identity = x =>
  x

const curry = (f = identity, arity = f.length) => x =>
{
  const next = (xs = []) =>
    xs.length >= arity
      ? f (...xs)
      : x => next ([ ...xs, x ])
  return next ([ x ])
}

const foo = (a, b, c) =>
  console.log ('a', a, 'b', b, 'c', c)

curry (foo) (1) (2) (3)
// 'a' 1 'b' 2 'c' 3

curry (foo) ('choo') ('bye') ()
// 'a' 'choo' 'b' 'bye' 'c' undefined

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