Backbone.Models this.get()复制整个数组或指向内存中的同一个数组

Question

 Person = Backbone.Model.extend({
        defaults: {
            name: 'Fetus',
            age: 0,
            children: []
        },
        initialize: function(){
            alert("Welcome to this world");
        },
        adopt: function( newChildsName ){
            var children_array = this.get("children");
            children_array.push( newChildsName );
            this.set({ children: children_array });
        }
    });

    var person = new Person({ name: "Thomas", age: 67, children: ['Ryan']});
    person.adopt('John Resig');
    var children = person.get("children"); // ['Ryan', 'John Resig']

在此示例代码中,我们有:

children_array = this.get("children")

我以为这只会指向内存中的相同数组(因此也是O(1)).然而,我认为这将是一个设计层,因为可以在不使用this.set()的情况下操纵数组,然后事件监听器就不会触发.

所以我猜它(不知何故神奇地)复制数组？

http://backbonejs.org/#Model-set

怎么了？

编辑:我刚刚在https://github.com/documentcloud/backbone/blob/master/backbone.js的骨干源代码中找到了实现(我在底部粘贴了相关代码)

获得回报:

return this.attributes[attr]

所以这只会指向内存中的相同数组吗？所以可以在不使用set()的情况下更改数组,这样会很糟糕......？我对么？

get: function(attr) {
      return this.attributes[attr];
    },

    // Get the HTML-escaped value of an attribute.
    escape: function(attr) {
      var html;
      if (html = this._escapedAttributes[attr]) return html;
      var val = this.get(attr);
      return this._escapedAttributes[attr] = _.escape(val == null ? '' : '' + val);
    },

    // Returns `true` if the attribute contains a value that is not null
    // or undefined.
    has: function(attr) {
      return this.get(attr) != null;
    },

    // Set a hash of model attributes on the object, firing `"change"` unless
    // you choose to silence it.
    set: function(key, value, options) {
      var attrs, attr, val;

      // Handle both `"key", value` and `{key: value}` -style arguments.
      if (_.isObject(key) || key == null) {
        attrs = key;
        options = value;
      } else {
        attrs = {};
        attrs[key] = value;
      }

      // Extract attributes and options.
      options || (options = {});
      if (!attrs) return this;
      if (attrs instanceof Model) attrs = attrs.attributes;
      if (options.unset) for (attr in attrs) attrs[attr] = void 0;

      // Run validation.
      if (!this._validate(attrs, options)) return false;

      // Check for changes of `id`.
      if (this.idAttribute in attrs) this.id = attrs[this.idAttribute];

      var changes = options.changes = {};
      var now = this.attributes;
      var escaped = this._escapedAttributes;
      var prev = this._previousAttributes || {};

      // For each `set` attribute...
      for (attr in attrs) {
        val = attrs[attr];

        // If the new and current value differ, record the change.
        if (!_.isEqual(now[attr], val) || (options.unset && _.has(now, attr))) {
          delete escaped[attr];
          (options.silent ? this._silent : changes)[attr] = true;
        }

        // Update or delete the current value.
        options.unset ? delete now[attr] : now[attr] = val;

        // If the new and previous value differ, record the change.  If not,
        // then remove changes for this attribute.
        if (!_.isEqual(prev[attr], val) || (_.has(now, attr) !== _.has(prev, attr))) {
          this.changed[attr] = val;
          if (!options.silent) this._pending[attr] = true;
        } else {
          delete this.changed[attr];
          delete this._pending[attr];
        }
      }

      // Fire the `"change"` events.
      if (!options.silent) this.change(options);
      return this;
    },

Answer 1

记录的界面实际上并没有指定谁拥有数组引用,所以你自己就在这里.如果你看一下实现,你会看到(正如你所做的那样)get直接从模型的内部返回一个引用attributes.这对于不可变类型(例如数字,字符串和布尔值)都可以正常工作,但是遇到了诸如数组之类的可变类型的问题:您可以轻松地更改某些内容,而无需Backbone知道它.

骨干模型似乎旨在包含原始类型.

有三个理由要求set:

1. 这就是接口规范所要做的.
2. 如果您不打电话set,则不会触发事件.
3. 如果你不打电话set,你将绕过有的验证逻辑set.

如果您正在处理数组和对象值,则必须小心.

请注意,这种行为get和set是一个实现细节,未来的版本可能会更聪明地处理它们如何处理非原始属性值.

数组属性(以及对象属性)的情况实际上比您最初怀疑的要糟糕.当你说m.set(p, v),如果拔出一个数组,Backbone将不会认为这set是一个改变v === current_value_of_p:

var a = m.get(p);

然后修改它:

a.push(x);

并将其发回:

m.set(p, a);

你不会"change"从模型中得到一个事件,因为a === a; Backbone 实际上使用了 Underscore isEqual,!==但在这种情况下效果是一样的.

例如,这个简单的chicanery:

var M = Backbone.Model.extend({});
var m = new M({ p: [ 1 ] });
m.on('change', function() { console.log('changed') });

console.log('Set to new array');
m.set('p', [2]);

console.log('Change without set');
m.get('p').push(3);

console.log('Get array, change, and re-set it');
var a = m.get('p'); a.push(4); m.set('p', a);

console.log('Get array, clone it, change it, set it');
a = _(m.get('p')).clone(); a.push(5); m.set('p', a);?

产生两个"change"事件:一个在第set一个之后,一个在最后一个之后set.

演示:http://jsfiddle.net/ambiguous/QwZDv/

如果你看一下set你会注意到对Backbone.Models 属性有一些特殊处理.

这里的基本教训很简单:

如果您打算使用可变类型作为属性值,那么如果您有可能更改该值,那么_.clone它们将在出路(或者$.extend(true, ...)如果您需要深层复制时使用).