[Vue源码剖析]如何实现组件

// 方式一
var MyComponent = Vue.extend({
    name: 'my-component',
    template: '<div>A custom component!</div>'
});
Vue.component('my-component', MyComponent);

// 方式二
Vue.component('my-component', {
    name: 'my-component',
    template: '<div>A custom component!</div>'
});

// 使用组件
<div id="example">
    <my-component></my-component>
</div>

Vue.extend = function (extendOptions) {
  extendOptions = extendOptions || {};
  var Super = this;
  var isFirstExtend = Super.cid === 0;
  if (isFirstExtend && extendOptions._Ctor) {
    return extendOptions._Ctor;
  }
  var name = extendOptions.name || Super.options.name;
  // 如果有name属性，即组件名称，检测name拼写是否合法
  if ('development' !== 'production') {
    if (!/^[a-zA-Z][\w-]*$/.test(name)) {
      warn('Invalid component name: "' + name + '". Component names ' + 'can only contain alphanumeric characaters and the hyphen.');
      name = null;
    }
  }
  // 创建一个VueComponent 构造函数，函数名为‘VueComponent’或者name
  var Sub = createClass(name || 'VueComponent');
  // 构造函数原型继承Vue.prototype
  Sub.prototype = Object.create(Super.prototype);
  Sub.prototype.constructor = Sub;
  Sub.cid = cid++;
  // 合并Vue.options和extendOptions，作为新构造函数的静态属性options   
  Sub.options = mergeOptions(Super.options, extendOptions);
  //'super'静态属性指向Vue函数
  Sub['super'] = Super;
  // start-----------------拷贝Vue静态方法   
  // allow further extension
  Sub.extend = Super.extend;
  // create asset registers, so extended classes
  // can have their private assets too.
  config._assetTypes.forEach(function (type) {
    Sub[type] = Super[type];
  });
  // end-----------------拷贝Vue静态方法   
  // enable recursive self-lookup
  if (name) {
    Sub.options.components[name] = Sub;
  }
  // cache constructor：缓存该构造函数
  if (isFirstExtend) {
    extendOptions._Ctor = Sub;
  }
  return Sub;
};

// _assetTypes: ['component', 'directive', 'elementDirective', 'filter', 'transition', 'partial']
config._assetTypes.forEach(function (type) {
  // 静态方法Vue.component
  Vue[type] = function (id, definition) {
    if (!definition) {
      return this.options[type + 's'][id];
    } else {
      /* istanbul ignore if */
      if ('development' !== 'production') {
        if (type === 'component' && (commonTagRE.test(id) || reservedTagRE.test(id))) {
          warn('Do not use built-in or reserved HTML elements as component ' + 'id: ' + id);
        }
      }
     // 如果第二个参数是简单对象，则需要通过Vue.extend创建组件构造函数
      if (type === 'component' && isPlainObject(definition)) {
        if (!definition.name) {
          definition.name = id;
        }
        definition = Vue.extend(definition);
      }
     // 将组件函数加入Vue静态属性options.components中，也就是，全局注入该组件
      this.options[type + 's'][id] = definition;
      return definition;
    }
  };
});

var MyComponent = Vue.extend({
    template: '<div>A custom component!</div>'
});

new Vue({
    el: '#example',
    components: {
        'my-component': MyComponent,
        'other-component': {
            template: '<div>A custom component!</div>'
        }
    }
});

Vue.prototype._init = function (options) {
    options = options || {};
    ....
    // merge options.
    options = this.$options = mergeOptions(this.constructor.options, options, this);
    ...
};

function mergeOptions(parent, child, vm) {
    //解析components属性
    guardComponents(child);
    guardProps(child);
    ...
}

function guardComponents(options) {
    if (options.components) {
        // 将对象转为数组
        var components = options.components = guardArrayAssets(options.components);
        //ids数组包含组件名
        var ids = Object.keys(components);
        var def;
        if ('development' !== 'production') {
            var map = options._componentNameMap = {};
        }
        // 遍历组件数组
        for (var i = 0, l = ids.length; i < l; i++) {
            var key = ids[i];
            if (commonTagRE.test(key) || reservedTagRE.test(key)) {
                'development' !== 'production' && warn('Do not use built-in or reserved HTML elements as component ' + 'id: ' + key);
                continue;
            }
            // record a all lowercase <-> kebab-case mapping for
            // possible custom element case error warning
            if ('development' !== 'production') {
                map[key.replace(/-/g, '').toLowerCase()] = hyphenate(key);
            }
            def = components[key];
            // 如果是组件定义是简单对象-对象字面量，那么需要根据该对象创建组件函数
            if (isPlainObject(def)) {
                components[key] = Vue.extend(def);
            }
        }
    }
}