JavaScript 自定义事件的实现

逆葵

发布于 2019-04-25 11:13:09

7780

发布于 2019-04-25 11:13:09

文章被收录于专栏：FECodingFECoding

自定义事件，就是有别于有别于带有浏览器特定行为的事件（类似 click, mouseover, submit, keydown 等事件），事件名称可以随意定义，可以通过特定的方法进行添加，触发以及删除。

模拟实现

1. 字面量实现

// 实现
var Event = {
    // 用于存储各种事件的回调函数
    _listeners: {},    
    // 添加
    addEvent: function(type, fn) {
        if (typeof this._listeners[type] === "undefined") {
            this._listeners[type] = [];
        }
        if (typeof fn === "function") {
            this._listeners[type].push(fn);
        }    
        return this;
    },
    // 触发
    fireEvent: function(type) {
        var arrayEvent = this._listeners[type];
        if (arrayEvent instanceof Array) {
            for (var i=0, length=arrayEvent.length; i<length; i+=1) {
                if (typeof arrayEvent[i] === "function") {
                    arrayEvent[i]({ type: type });    
                }
            }
        }    
        return this;
    },
    // 删除
    removeEvent: function(type, fn) {
    	var arrayEvent = this._listeners[type];
        if (typeof type === "string" && arrayEvent instanceof Array) {
            if (typeof fn === "function") {
                // 清除当前 type 类型事件下对应 fn 方法
                for (var i=0, length=arrayEvent.length; i<length; i+=1){
                    if (arrayEvent[i] === fn){
                        this._listeners[type].splice(i, 1);
                        break;
                    }
                }
            } else {
                // 如果参数仅含 type, 或参数 fn 邪魔外道，则所有 type 类型事件清除
                delete this._listeners[type];
            }
        }
        return this;
    }
};

// 调用
Event.addEvent("alert", function() {
    alert("弹出！");
});

// 触发自定义 alert 事件
Event.fireEvent("alert");

缺点：字面量实现其属性方法等都是暴露而且都是唯一的，一旦某个关键属性(如 _listeners)不小心在某事件处 reset 了下，则整个全局的自定义事件都会崩溃。

2. 原型模式实现

// 实现
var EventTarget = function() {
    this._listener = {};
};

EventTarget.prototype = {
    constructor: this,
    addEvent: function(type, fn) {
        if (typeof type === "string" && typeof fn === "function") {
            if (typeof this._listener[type] === "undefined") {
                this._listener[type] = [fn];
            } else {
                this._listener[type].push(fn);    
            }
        }
        return this;
    },
    addEvents: function(obj) {
        obj = typeof obj === "object"? obj : {};
        var type;
        for (type in obj) {
            if ( type && typeof obj[type] === "function") {
                this.addEvent(type, obj[type]);    
            }
        }
        return this;
    },
    fireEvent: function(type) {
        if (type && this._listener[type]) {
            var events = {
                type: type,
                target: this    
            };
            
            for (var length = this._listener[type].length, start=0; start<length; start+=1) {
                this._listener[type][start].call(this, events);
            }
        }
        return this;
    },
    fireEvents: function(array) {
        if (array instanceof Array) {
            for (var i=0, length = array.length; i<length; i+=1) {
                this.fireEvent(array[i]);
            }
        }
        return this;
    },
    removeEvent: function(type, key) {
        var listeners = this._listener[type];
        if (listeners instanceof Array) {
            if (typeof key === "function") {
                for (var i=0, length=listeners.length; i<length; i+=1){
                    if (listeners[i] === key){
                        listeners.splice(i, 1);
                        break;
                    }
                }
            } else if (key instanceof Array) {
                for (var lis=0, lenkey = key.length; lis<lenkey; lis+=1) {
                    this.removeEvent(type, key[lenkey]);
                }
            } else {
                delete this._listener[type];
            }
        }
        return this;
    },
    removeEvents: function(params) {
        if (params instanceof Array) {
            for (var i=0, length = params.length; i<length; i+=1) {
                this.removeEvent(params[i]);
            }    
        } else if (typeof params === "object") {
            for (var type in params) {
                this.removeEvent(type, params[type]);    
            }
        }
        return this;    
    }
};

// 调用
var myEvents = new EventTarget();
var yourEvents = new EventTarget();

浏览器 API 实现

1. 创建自定义事件

var event = new Event('build');

// Listen for the event.
elem.addEventListener('build', function (e) { ... }, false);

// Dispatch the event.
elem.dispatchEvent(event);

添加自定义数据 – CustomEvent()

var event = new CustomEvent('build', { 'detail': elem.dataset.time });

下面的代码允许你在事件监听器中访问更多的数据：

function eventHandler(e) {
  log('The time is: ' + e.detail);
}

2. 老式方法（已过时，此处仅作参考）

// Create the event.
var event = document.createEvent('Event');

// Define that the event name is 'build'.
event.initEvent('build', true, true);

// Listen for the event.
document.addEventListener('build', function (e) {
  // e.target matches document from above
}, false);

// target can be any Element or other EventTarget.
document.dispatchEvent(event);