add event.js

fltenwall · fltenwall · commit 5e718d0b369b · 2021-06-09T23:44:52.000+08:00
diff --git a/events.js b/events.js
@@ -0,0 +1,45 @@
+function EventEmitter(){
+    this._events = {};
+}
+
+EventEmitter.prototype.on = function(eventName,callback){
+    // if(eventName !== 'newListener'){
+    //     this._events['newListener'] ? this._events['newListener'].forEach(fn => fn(eventName)) : void 0
+    // }
+    if(!this._events){
+        // this._events = {};这种方式有原型链
+        this._events = Object.create(null);
+    }
+    if(this._events[eventName]){
+        this._events[eventName].push(callback);
+    }else{
+        this._events[eventName] = [callback];
+    }
+}
+
+EventEmitter.prototype.once = function(eventName,callback){
+    function one(){
+        callback(...arguments);
+        this.off(eventName,one);
+    }
+    one.link = callback;
+    this.on(eventName,one);
+}
+
+EventEmitter.prototype.off = function(eventName,callback){
+    if(this._events[eventName]){
+        this._events[eventName] = this._events[eventName].filter(fn => {
+            fn != callback && fn.link != callback //为once做处理
+        })    
+    }
+}
+
+EventEmitter.prototype.emit = function(eventName){
+    if(this._events[eventName]){
+        this._events[eventName].forEach(fn => {
+            fn.call(this,...arguments);
+        });
+    }
+}
+
+module.exports = EventEmitter;
