洋葱模型编程

考虑3层洋葱模型，A、B、C。

A层：

var middlewareA = function (ins) {
  return function (next) {
    return function (payload) {
      // some operations here ...
      var result = next(payload);
      // some operations here ...
      return result;
    }
  }
}

B层：

var middlewareB = function (ins) {
  return function (next) {
    return function (payload) {
      // some operations here ...
      var result = next(payload);
      // some operations here ...
      return result;
    }
  }
}

C层实际上是洋葱模型的内核：

var middlewareC = function (ins) {
  return function () {
    return function (payload) {
      // some operations here ...
      return operate(payload);
    }
  }
}

从C层到A层回溯分析：

var mcPayloadHandler = middlewareC(ins)();
var mbPayloadHandler = middlewareB(ins)(mcPayloadHandler);
var maPayloadHandler = middlewareA(ins)(mbPayloadHandler);
var finalResult = maPayloadHandler(payload);

用回调金字塔写的话，就像这样：

var f = middlewareA(ins)(
  middlewareB(ins)(
    middlewareC(ins)()
  )
);
var finalResult = f(payload);

在线demo：https://repl.it/Ca3K/0

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