express框架route.js源码解析

function Route(path) {
  this.path = path;
  this.stack = [];
  // route handlers for various http methods
  this.methods = {};
}

Route.prototype.dispatch = function dispatch(req, res, done) {//done是router的next函数，执行后会跳到下一个中间件，从而跳过当前route的stack中剩下的函数
  var idx = 0;
  var stack = this.stack;
  if (stack.length === 0) { 
    return done();//done是开始执行该路由组件时传进来的回调，执行完路由栈里的函数后执行done
  }

  var method = req.method.toLowerCase();
  if (method === 'head' && !this.methods['head']) {
    method = 'get';
  }

  req.route = this;

  next();

  function next(err) {
    if (err && err === 'route') {//使用next('route')会不执行剩下的函数
      return done();
    }

    var layer = stack[idx++];
    if (!layer) {//已经遍历完layer了，跳到下一个router中的layer
      return done(err);
    }

    if (layer.method && layer.method !== method) {//方法不匹配,next
      return next(err);
    }

    if (err) {//通过层层筛选，最后可以执行的路由函数，先判断有没有错误，再执行相应的函数，每个layer都有对应的回调。
      layer.handle_error(err, req, res, next);
    } else {
      layer.handle_request(req, res, next);
    }
  }
};

Route.prototype.all = function all() {
  var handles = flatten(slice.call(arguments));

  for (var i = 0; i < handles.length; i++) {
    var handle = handles[i];

    if (typeof handle !== 'function') {
      var type = toString.call(handle);
      var msg = 'Route.all() requires callback functions but got a ' + type;
      throw new TypeError(msg);
    }

    var layer = Layer('/', {}, handle);
    layer.method = undefined;

    this.methods._all = true;
    this.stack.push(layer);
  }

  return this;
};