道格拉斯·克罗克福德(Douglas Crockford）的“Javascript:The Good Parts”第5.

Douglas Crockford's “Javascript: The Good Parts” Chapter 5.5

本文关键字：The Javascript Good Parts 克罗 格拉斯 Crockford Douglas 道格拉      更新时间：2023-09-26

这与这个问题非常相似

我的问题更多是关于示例代码。

法典：

var eventuality = function (that) {
    var registry = {};
    that.fire = function (event) {
// Fire an event on an object. The event can be either
// a string containing the name of the event or an
// object containing a type property containing the
// name of the event. Handlers registered by the 'on'
// method that match the event name will be invoked.
        var array,
            func,
            handler,
            i,
            type = typeof event === 'string' ?
                    event : event.type;
// If an array of handlers exist for this event, then
// loop through it and execute the handlers in order.
        if (registry.hasOwnProperty(type)) {
            array = registry[type];
            for (i = 0; i < array.length; i += 1) {
                handler = array[i];
// A handler record contains a method and an optional
// array of parameters. If the method is a name, look
// up the function.
                func = handler.method;
                if (typeof func === 'string') {
                    func = this[func];
                }
// Invoke a handler. If the record contained
// parameters, then pass them. Otherwise, pass the
// event object.
                func.apply(this,
                    handler.parameters || [event]);
            }
        }
        return this;
    };
    that.on = function (type, method, parameters) {
// Register an event. Make a handler record. Put it
// in a handler array, making one if it doesn't yet
// exist for this type.
        var handler = {
            method: method,
            parameters: parameters
        };
        if (registry.hasOwnProperty(type)) {
            registry[type].push(handler);
        } else {
            registry[type] = [handler];
        }
        return this;
    };
    return that;
}

在代码中，我不明白这一行，func = handler.method;。

这怎么能工作？我的意思是handler.method应该是未定义的，对吧？

谢谢

这里

定义了handler.method（当然它必须作为参数传入）：

that.on = function (type, method, parameters) {
    var handler = {
        method: method,   // defines the method property of the handler object
        parameters: parameters  // defines the parameters property of the handler object
    };

阅读 MDN 上的使用对象 - .method引用handler对象的 method 属性

handler是存储在registry中的对象：

    array = registry[type];
    for (i = 0; i < array.length; i += 1) {
        handler = array[i];

它是在that.on方法中添加的：

    var handler = {
        method: method,
        parameters: parameters
    };
    if (registry.hasOwnProperty(type)) {
        registry[type].push(handler);
    } else {
        registry[type] = [handler];
    }

它显然具有method属性。

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