add array function

Author: Steffan

src/EventManager.js

@@ -2,7 +2,7 @@
  * Event manager class.
  */
 
-import {isArray, isUndefined} from './util';
+import {array, isArray, isUndefined} from './util';
 
 export default class EventManager {
 
@@ -12,7 +12,7 @@ export default class EventManager {
 
     on(event, callback, priority = 0) {
 
-        const listeners = this.listeners[event] || [];
+        const listeners = array(this.listeners[event]);
         const index = listeners.findIndex(listener => listener.priority < priority);
 
         if (~index) {

src/util.js

@@ -18,43 +18,44 @@ export function forEach(collection, callback) {
     });
 }
 
-/**
- * Array.findIndex() polyfill.
- */
-if (!Array.prototype.findIndex) {
+export function array(array = []) {
 
-    // eslint-disable-next-line
-    Object.defineProperty(Array.prototype, 'findIndex', {
+    if (!array.findIndex) {
+        array.findIndex = findIndex;
+    }
 
-        value(predicate) {
-
-            if (this == null) {
-                throw new TypeError('"this" is null or not defined');
-            }
+    return array;
+}
 
-            if (typeof predicate !== 'function') {
-                throw new TypeError('predicate must be a function');
-            }
+/**
+ * Array.findIndex() polyfill.
+ */
+function findIndex(predicate) {
 
-            const o = Object(this);
-            const len = o.length >>> 0;
-            const thisArg = arguments[1];
+    if (this == null) {
+        throw new TypeError('"this" is null or not defined');
+    }
 
-            let k = 0;
+    if (typeof predicate !== 'function') {
+        throw new TypeError('predicate must be a function');
+    }
 
-            while (k < len) {
+    const o = Object(this);
+    const len = o.length >>> 0;
+    const thisArg = arguments[1];
 
-                const kValue = o[k];
+    let k = 0;
 
-                if (predicate.call(thisArg, kValue, k, o)) {
-                    return k;
-                }
+    while (k < len) {
 
-                k++;
-            }
+        const kValue = o[k];
 
-            return -1;
+        if (predicate.call(thisArg, kValue, k, o)) {
+            return k;
         }
 
-    });
+        k++;
+    }
+
+    return -1;
 }