[蔡小北-每日一题](Event)用原生js实现自定义事件(2022-02-10)

JS自定义事件

Javascript自定义事件类似设计的观察者模式，通过状态的变更来监听行为，主要功能解耦、易于扩展。多用于组件、模块间的交互。

具体实现如下：

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]) {
            //event参数设置
            var events = {
                type: type,
                target: this
            };

            for (var length = this._listener[type].length, start=0; start<length; start+=1) {
                //改变this指向
                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;
    }
};