Function initComputed

vue.js:5040–5080

(vm, computed)

    //初始化计算属性 并且判断属性的key 是否 在 data ，将 计算属性的key 添加入监听者中
    function initComputed(vm, computed) {
        // $flow-disable-line
        //创建一个新的监听者对象空对象
        var watchers = vm._computedWatchers = Object.create(null);
        // computed properties are just getters during SSR 计算的属性只是SSR期间的getter
        var isSSR = isServerRendering(); // 服务器呈现  判断是不是node 服务器环境

        for (var key in computed) {
            var userDef = computed[key]; //获取值
            var getter = typeof userDef === 'function' ? userDef : userDef.get; //获取值函数
            if ("development" !== 'production' && getter == null) { //如果getter 是 空 警告
                warn(
                    ("Getter is missing for computed property \"" + key + "\"."),
                    vm
                );
            }

            if (!isSSR) { //如果不是node ssr渲染
                // create internal watcher for the computed property.
                watchers[key] = new Watcher(
                    vm, //vm  vode
                    getter || noop,  //函数
                    noop,  //回调函数
                    computedWatcherOptions  //参数 lazy = true
                );
            }

            // component-defined computed properties are already defined on the 组件定义的计算属性已经在
            // component prototype. We only need to define computed properties defined 组件原型。我们只需要定义已定义的计算属性
            // at instantiation here. 在实例化。
            if (!(key in vm)) { //如果computed 属性key 不在虚拟dom中
                defineComputed(vm, key, userDef); //定义计算属性 并且 把属性的数据 添加到对象监听中
            } else {
                if (key in vm.$data) {  //如果判断属性监听的key在 data 中则发出警告
                    warn(("The computed property \"" + key + "\" is already defined in data."), vm);
                } else if (vm.$options.props && key in vm.$options.props) {
                    warn(("The computed property \"" + key + "\" is already defined as a prop."), vm);
                }
            }
        }
    }

    //定义计算属性 并且 把属性的数据 添加到对象监听中
    function defineComputed(target, //目标