Replace the boolean args on EventTimeline methods with constants

lib/models/event-timeline.js

@@ -44,6 +44,18 @@ function EventTimeline(roomId) {
     this._paginationRequests = {'b': null, 'f': null};
 }
 
+/**
+ * Symbolic constant for methods which take a 'direction' argument:
+ * refers to the start of the timeline, or backwards in time.
+ */
+EventTimeline.BACKWARDS = "b";
+
+/**
+ * Symbolic constant for methods which take a 'direction' argument:
+ * refers to the end of the timeline, or forwards in time.
+ */
+EventTimeline.FORWARDS = "f";
+
 /**
  * Initialise the start and end state with the given events
  *
@@ -104,47 +116,65 @@ EventTimeline.prototype.getEvents = function() {
 /**
  * Get the room state at the start/end of the timeline
  *
- * @param {boolean} start true to get the state at the start of the timeline;
- * false to get the state at the end of the timeline.
+ * @param {string} direction   EventTimeline.BACKWARDS to get the state at the
+ *   start of the timeline; EventTimeline.FORWARDS to get the state at the end
+ *   of the timeline.
+ *
  * @return {RoomState} state at the start/end of the timeline
  */
-EventTimeline.prototype.getState = function(start) {
-    return start ? this._startState : this._endState;
+EventTimeline.prototype.getState = function(direction) {
+    if (direction == EventTimeline.BACKWARDS) {
+        return this._startState;
+    } else if (direction == EventTimeline.FORWARDS) {
+        return this._endState;
+    } else {
+        throw new Error("Invalid direction '" + direction + "'");
+    }
 };
 
 /**
  * Get a pagination token
  *
- * @param {boolean} backwards   true to get the pagination token for going
- *                                  backwards in time
+ * @param {string} direction   EventTimeline.BACKWARDS to get the pagination
+ *   token for going backwards in time; EventTimeline.FORWARDS to get the
+ *   pagination token for going forwards in time.
+ *
  * @return {?string} pagination token
  */
-EventTimeline.prototype.getPaginationToken = function(backwards) {
-    return this.getState(backwards).paginationToken;
+EventTimeline.prototype.getPaginationToken = function(direction) {
+    return this.getState(direction).paginationToken;
 };
 
 /**
  * Set a pagination token
  *
  * @param {?string} token       pagination token
- * @param {boolean} backwards   true to set the pagination token for going
- *                                   backwards in time
+ *
+ * @param {string} direction    EventTimeline.BACKWARDS to set the pagination
+ *   token for going backwards in time; EventTimeline.FORWARDS to set the
+ *   pagination token for going forwards in time.
  */
-EventTimeline.prototype.setPaginationToken = function(token, backwards) {
-    this.getState(backwards).paginationToken = token;
+EventTimeline.prototype.setPaginationToken = function(token, direction) {
+    this.getState(direction).paginationToken = token;
 };
 
 /**
  * Get the next timeline in the series
  *
- * @param {boolean} before  true to get the previous timeline; false to get the
- *                                   following one
+ * @param {string} direction EventTimeline.BACKWARDS to get the previous
+ *   timeline; EventTimeline.FORWARDS to get the next timeline.
  *
  * @return {?EventTimeline} previous or following timeline, if they have been
  * joined up.
  */
-EventTimeline.prototype.getNeighbouringTimeline = function(before) {
-    return before ? this._prevTimeline : this._nextTimeline;
+EventTimeline.prototype.getNeighbouringTimeline = function(direction) {
+    if (direction == EventTimeline.BACKWARDS) {
+        return this._prevTimeline;
+    } else if (direction == EventTimeline.FORWARDS) {
+        return this._nextTimeline;
+    } else {
+        throw new Error("Invalid direction '" + direction + "'");
+    }
 };
 
 /**
@@ -152,25 +182,28 @@ EventTimeline.prototype.getNeighbouringTimeline = function(before) {
  *
  * @param {EventTimeline} neighbour previous/following timeline
  *
- * @param {boolean} before true to set the previous timeline; false to set
- * following one.
+ * @param {string} direction EventTimeline.BACKWARDS to set the previous
+ *   timeline; EventTimeline.FORWARDS to set the next timeline.
  *
  * @throws {Error} if an attempt is made to set the neighbouring timeline when
  * it is already set.
  */
-EventTimeline.prototype.setNeighbouringTimeline = function(neighbour, before) {
-    if (this.getNeighbouringTimeline(before)) {
+EventTimeline.prototype.setNeighbouringTimeline = function(neighbour, direction) {
+    if (this.getNeighbouringTimeline(direction)) {
         throw new Error("timeline already has a neighbouring timeline - " +
                         "cannot reset neighbour");
     }
-    if (before) {
+
+    if (direction == EventTimeline.BACKWARDS) {
         this._prevTimeline = neighbour;
-    } else {
+    } else if (direction == EventTimeline.FORWARDS) {
         this._nextTimeline = neighbour;
+    } else {
+        throw new Error("Invalid direction '" + direction + "'");
     }
 
     // make sure we don't try to paginate this timeline
-    this.setPaginationToken(null, before);
+    this.setPaginationToken(null, direction);
 };
 
 /**