Duplicate code -> EventEmitter

copied from node

_build_js.sh

@@ -18,6 +18,7 @@ npm run babel -- -o "out/js/app.$FRONT_END_HASH.js" ${smarg} js/lib \
     js/lib/chibi.js \
     js/lib/keymaster.js \
     js/lib/polyfills.js \
+    js/event_emitter.js \
     js/utils.js \
     js/modal.js \
     js/notif.js \

js/demo.js

@@ -304,47 +304,7 @@ class ScrollingTerminal {
   }
 }
 
-class Process {
-  constructor (args) {
-    // event listeners
-    this._listeners = {}
-  }
-  on (event, listener) {
-    if (!this._listeners[event]) this._listeners[event] = []
-    this._listeners[event].push({ listener })
-  }
-  once (event, listener) {
-    if (!this._listeners[event]) this._listeners[event] = []
-    this._listeners[event].push({ listener, once: true })
-  }
-  off (event, listener) {
-    let listeners = this._listeners[event]
-    if (listeners) {
-      for (let i in listeners) {
-        if (listeners[i].listener === listener) {
-          listeners.splice(i, 1)
-          break
-        }
-      }
-    }
-  }
-  emit (event, ...args) {
-    let listeners = this._listeners[event]
-    if (listeners) {
-      let remove = []
-      for (let listener of listeners) {
-        try {
-          listener.listener(...args)
-          if (listener.once) remove.push(listener)
-        } catch (err) {
-          console.error(err)
-        }
-      }
-      for (let listener of remove) {
-        listeners.splice(listeners.indexOf(listener), 1)
-      }
-    }
-  }
+class Process extends EventEmitter {
   write (data) {
     this.emit('in', data)
   }

js/event_emitter.js

@@ -0,0 +1,70 @@
+if (!('EventEmitter' in window)) {
+  window.EventEmitter = class EventEmitter {
+    constructor () {
+      this._listeners = {}
+    }
+
+    /**
+     * Bind an event listener to an event
+     * @param {string} event - the event name
+     * @param {Function} listener - the event listener
+     */
+    on (event, listener) {
+      if (!this._listeners[event]) this._listeners[event] = []
+      this._listeners[event].push({ listener })
+    }
+
+    /**
+     * Bind an event listener to be run only once the next time the event fires
+     * @param {string} event - the event name
+     * @param {Function} listener - the event listener
+     */
+    once (event, listener) {
+      if (!this._listeners[event]) this._listeners[event] = []
+      this._listeners[event].push({ listener, once: true })
+    }
+
+    /**
+     * Remove an event listener
+     * @param {string} event - the event name
+     * @param {Function} listener - the event listener
+     */
+    off (event, listener) {
+      let listeners = this._listeners[event]
+      if (listeners) {
+        for (let i in listeners) {
+          if (listeners[i].listener === listener) {
+            listeners.splice(i, 1)
+            break
+          }
+        }
+      }
+    }
+
+    /**
+     * Emits an event
+     * @param {string} event - the event name
+     * @param {...any} args - arguments passed to all listeners
+     */
+    emit (event, ...args) {
+      let listeners = this._listeners[event]
+      if (listeners) {
+        let remove = []
+        for (let listener of listeners) {
+          try {
+            listener.listener(...args)
+            if (listener.once) remove.push(listener)
+          } catch (err) {
+            console.error(err)
+          }
+        }
+
+        // this needs to be done in this roundabout way because for loops
+        // do not like arrays with changing lengths
+        for (let listener of remove) {
+          listeners.splice(listeners.indexOf(listener), 1)
+        }
+      }
+    }
+  }
+}

js/term_screen.js

@@ -68,8 +68,10 @@ for (let gray = 0; gray < 24; gray++) {
   colorTable256.push(`rgb(${value}, ${value}, ${value})`)
 }
 
-window.TermScreen = class TermScreen {
+window.TermScreen = class TermScreen extends EventEmitter {
   constructor () {
+    super()
+
     this.canvas = mk('canvas')
     this.ctx = this.canvas.getContext('2d')
 
@@ -145,9 +147,6 @@ window.TermScreen = class TermScreen {
     // mouse features
     this.mouseMode = { clicks: false, movement: false }
 
-    // event listeners
-    this._listeners = {}
-
     // make writing to window update size and draw
     const self = this
     this.window = new Proxy(this._window, {
@@ -350,69 +349,6 @@ window.TermScreen = class TermScreen {
     })
   }
 
-  /**
-   * Bind an event listener to an event
-   * @param {string} event - the event name
-   * @param {Function} listener - the event listener
-   */
-  on (event, listener) {
-    if (!this._listeners[event]) this._listeners[event] = []
-    this._listeners[event].push({ listener })
-  }
-
-  /**
-   * Bind an event listener to be run only once the next time the event fires
-   * @param {string} event - the event name
-   * @param {Function} listener - the event listener
-   */
-  once (event, listener) {
-    if (!this._listeners[event]) this._listeners[event] = []
-    this._listeners[event].push({ listener, once: true })
-  }
-
-  /**
-   * Remove an event listener
-   * @param {string} event - the event name
-   * @param {Function} listener - the event listener
-   */
-  off (event, listener) {
-    let listeners = this._listeners[event]
-    if (listeners) {
-      for (let i in listeners) {
-        if (listeners[i].listener === listener) {
-          listeners.splice(i, 1)
-          break
-        }
-      }
-    }
-  }
-
-  /**
-   * Emits an event
-   * @param {string} event - the event name
-   * @param {...any} args - arguments passed to all listeners
-   */
-  emit (event, ...args) {
-    let listeners = this._listeners[event]
-    if (listeners) {
-      let remove = []
-      for (let listener of listeners) {
-        try {
-          listener.listener(...args)
-          if (listener.once) remove.push(listener)
-        } catch (err) {
-          console.error(err)
-        }
-      }
-
-      // this needs to be done in this roundabout way because for loops
-      // do not like arrays with changing lengths
-      for (let listener of remove) {
-        listeners.splice(listeners.indexOf(listener), 1)
-      }
-    }
-  }
-
   /**
    * The color palette. Should define 16 colors in an array.
    * @type {number[]}