Coffeescript类比Backbone扩展更加膨胀

Question

我刚刚开始学习Coffeescript,并且无法找到我应该使用的确切答案

class Model extends Backbone.Model
    urlRoot: '//some/url'

编译成

Model = (function(_super) {
    __extends(Model, _super);

    function Model() {
        _ref = Model.__super__.constructor.apply(this, arguments);
        return _ref;
    }

    Model.prototype.urlRoot = '//some/url';

    return Model;

})(Backbone.Model);

而不是

Model = Backbone.Model.extend
    urlRoot: '//some/url'

编译成

var Model = Backbone.Model.extend({
    urlRoot: '//some/url'
});

我问的主要原因是因为前者几乎用于我所看过的所有例子.但是,与后者相比,它在编译时会产生"更多"的膨胀.我确实读过这个问题,但答案似乎有所不同.

Answer 1

既然你只是在询问膨胀,那么让我们来看看一些代码.

用的JavaScript Backbone.Model.extend

如果打开Backbone源代码,您将看到该extend函数如下:

var extend = function(protoProps, staticProps) {
    var parent = this;
    var child;

    if (protoProps && _.has(protoProps, 'constructor')) { // _.has comes from
      child = protoProps.constructor;                     // underscore, even 
    } else {                                              // more 'bloat'
      child = function(){ return parent.apply(this, arguments); };
    }

    _.extend(child, parent, staticProps);                // more underscore

    var Surrogate = function(){ this.constructor = child; };
    Surrogate.prototype = parent.prototype;
    child.prototype = new Surrogate;

    if (protoProps) _.extend(child.prototype, protoProps);

    child.__super__ = parent.prototype;

    return child;
  };

这里实际发生了什么:

当我们打电话

var Model = Backbone.Model.extend({urlRoot: '//some/url' });

我们得到类似的东西:

  // Create new constructor which calls the parent constructor
  var Model;
  if (({}).hasOwnProperty.call({urlRoot: '//some/url' }, 'constructor') {
      // this is false so...                    
  } else {
      Model = function(){ return Backbone.Model.apply(this, arguments); };
  }

  // Set up prototype chain
  var Surrogate = function(){ this.constructor = model; };
  Surrogate.prototype = Backbone.Model.prototype;
  Model.prototype = new Surrogate;

  // Add properties to the child prototype
  // Same as:
  // Model.prototype.urlRoot = '//some/url';
  _.extend(Model.prototype, { urlRoot: '//some/url' });

  // Set the magical __super__ property
  Model.__super__ = Backbone.Model.prototype;

CoffeeScript用 extends

将其与CoffeeScript代码进行比较.您将看到当您使用extends名为__extendsgets 的魔法函数添加到文件的开头时(格式化时)如下所示:

__extends = function(child, parent) { 
    for (var key in parent) { 
        if (__hasProp.call(parent, key)) 
            child[key] = parent[key]; 
    }

    function ctor() { this.constructor = child; } 
    ctor.prototype = parent.prototype; 
    child.prototype = new ctor(); 

    child.__super__ = parent.prototype; 

    return child; 
};

这与生成的JS结合:

var Model = (function(_super) {
    __extends(Model, _super);

    function Model() {
        _ref = Model.__super__.constructor.apply(this, arguments);
        return _ref;
    }

    Model.prototype.urlRoot = '//some/url';

    return Model;

})(Backbone.Model);

这里实际发生了什么:

当我们打电话

Model extends Backbone.Model
    urlRoot: '//some/url'

我们得到类似的东西:

// Create new constructor which calls the parent constructor
var Model = function () {
    return Model.__super__.constructor.apply(this, arguments);
}

// Copy static properties from Backbone.Model to Model
for (var key in Backbone.Model) {
    if (__hasProp.call(Backbone.Model, key)) 
        Model[key] = Backbone.Model[key]; 
}

// Set up prototype chain
function ctor() { this.constructor = Model; } 
ctor.prototype = Backbone.Model.prototype; 
Model.prototype = new ctor(); 

// Add properties to the child prototype
Model.prototype.urlRoot = '//some/url';

// Set the magical __super__ property
Model.__super__ = Backbone.Model.prototype; 

我们看到了什么？

他们看起来很相似不是吗？

CoffeeScript只是JavaScript.如果您已经在使用Backbone并且想要避免__extends在生成的源中添加函数,那么请使用Backbone.Model.extend.如果你想避免在Backbone中加入所有内容,那么extends几乎可以做同样的事情.这么多例子不使用后者的原因是Backbone不需要使用CoffeeScript - 只是有一个依赖外部库的例子是没有意义的.