初始化

utils/eventEmitter.js

@@ -0,0 +1,18 @@
+export class EventEmitter {
+  constructor() {
+    this._events = Object.create(null)
+  }
+  on(type, fn) {
+    (this._events[type] || (this._events[type] = [])).push(fn)
+  }
+  emit(type, ...args) {
+    (this._events[type] || []).forEach(fn => fn(...args))
+  }
+  off(type, fn) {
+    if (!fn) this._events[type] = []
+    else {
+      const idx = (this._events[type] || []).indexOf(fn)
+      if (idx > -1) this._events[type].splice(idx, 1)
+    }
+  }
+}