update event emitter

Author: qieguo2016

js/array.js

@@ -301,4 +301,32 @@ function mapConcatTest() {
   var target = [['a', 'b', 'c'], ['a', 'b']];
   console.log('\nmapConcatTest:\n', mapConcat(target));
 }
-mapConcatTest()
+// mapConcatTest();
+
+
+// 求整数数组的最大子串和，如 [-23, 17, -7, 11, -2, 1, -34] 的最大子串和是21，对应子串是 [17, -7, 11]
+function maxSeqSum(arr) {
+    if (!Array.isArray(arr)) {
+        return null;
+    }
+    const len = arr.length;
+    let maxSum = arr[0];
+    let seqSum = arr[0];
+    for (let i = 1; i < len; i++) {
+        if (seqSum <= 0) {
+            seqSum = arr[i];
+        } else {
+            seqSum += arr[i];
+        }
+        if (seqSum > maxSum) {
+            maxSum = seqSum;
+        }
+    }
+    return maxSum;
+}
+function maxSeqSumTest() {
+    console.log(maxSeqSum([-23, 17, -7, 11, -2, 1, -34]));
+    console.log(maxSeqSum([1, -2, 3, 10, -4, 7, 2, -5]));
+    console.log(maxSeqSum([-1]));
+}
+// maxSeqSumTest();

js/event.js

@@ -5,56 +5,83 @@
  * @description : 一个简单的观察者模式事件系统实现
  */
 
-function EventHandle() {
-    var events = {};
-    this.on = function(event, callback) {
-        callback = callback || function() { };
-        if (typeof events[event] === 'undefined') {
-            events[event] = [callback];
+const Noop = () => {};
+
+class EventEmitter {
+    constructor() {
+        this.events = [];
+    }
+
+    on(event, handler = Noop) {
+        if (typeof this.events[event] === 'undefined') {
+            this.events[event] = [handler];
         } else {
-            events[event].push(callback);
+            this.events[event].push(handler);
         }
-    };
+    }
 
-    this.emit = function(event, args) {
-        if (typeof events[event] !== 'undefined') {
-            events[event].forEach(function(fn) {
-                fn(args);
-            });
+    once(event, handler = Noop) {
+        const once = `once_${event}`;
+        if (typeof this.events[once] === 'undefined') {
+            this.events[once] = [handler];
         } else {
-            throw new Error('event: ' + event + ', not found');
+            this.events[once].push(handler);
         }
-    };
+    }
+
+    emit(event, args) {
+        const once = `once_${event}`;
+        if (typeof this.events[once] !== 'undefined') {
+            this.events[once].forEach((handler) => {
+                handler(args);
+            });
+            delete this.events[`once_${event}`];
+        }
+        if (typeof this.events[event] !== 'undefined') {
+            this.events[event].forEach((handler) => {
+                handler(args);
+            });
+        }
+    }
 
-    this.off = function(event) {
-        if (typeof events[event] !== 'undefined') {
-            delete events[event];
+    off(event, handler) {
+        if (typeof this.events[event] !== 'undefined') {
+            if (!!handler) {
+                const index = this.events[event].indexOf(handler);
+                this.events[event].splice(index, 1);
+            } else {
+                delete this.events[event];
+            }
         }
     };
 }
 
 function test() {
-    var eh = new EventHandle();
+    const eh = new EventEmitter();
+
+    const firstHd = (str) => {console.log('first greet: ', str);};
 
-    eh.on('greet', function(str) {
-        console.log(str);
-    });
+    eh.on('greet', firstHd);
 
-    eh.on('greet', function(name) {
-        console.log(name + ', hello!');
-    });
+    eh.on('greet', (str) => {console.log('second greet: ', str);});
 
-    eh.on('bye', function(name) {
-        console.log(name + ', goodbye!');
-    });
+    eh.on('bye', (name) => {console.log(name + ', goodbye!');});
+
+    eh.once('break', (str) => {console.log(`once break: ${str}`);});
+    eh.on('break', (str) => {console.log(`on break: ${str}`);});
 
     console.log('======  start  ======');
     eh.emit('greet', 'Green');
     eh.emit('bye', 'Mark');
+    eh.emit('break', 'Jack');
+    eh.emit('break', 'Tony');
 
     console.log('======  removeListener  ======');
     eh.off('bye');
     eh.emit('bye', 'Mark');
+
+    eh.off('greet', firstHd);
+    eh.emit('greet', 'Green');
 }
 
 test();