Fixing CircularBuffer.unshift

circular-buffer.js

@@ -68,15 +68,21 @@ CircularBuffer.prototype.push = function(item) {
  * @return {number}      - Returns the new size of the buffer.
  */
 CircularBuffer.prototype.unshift = function(item) {
-  if (this.size === this.capacity)
-    throw new Error('mnemonist/circular-buffer.unshift: buffer capacity (' + this.capacity + ') exceeded!');
-
   var index = this.start - 1;
 
   if (this.start === 0)
     index = this.capacity - 1;
 
   this.items[index] = item;
+
+  // Overwriting
+  if (this.size === this.capacity) {
+
+    this.start = index;
+
+    return this.size;
+  }
+
   this.start = index;
 
   return ++this.size;

test/circular-buffer.js

@@ -35,7 +35,7 @@ describe('CircularBuffer', function() {
     assert.strictEqual(buffer.capacity, 10);
   });
 
-  it('should be possible to wrap buffer around.', function() {
+  it('should be possible to wrap buffer around when pushing.', function() {
     var buffer = new CircularBuffer(Array, 3);
 
     buffer.push(1);
@@ -63,6 +63,34 @@ describe('CircularBuffer', function() {
     assert.strictEqual(buffer.size, 3);
   });
 
+  it('should be possible to wrap buffer around when unshifting.', function() {
+    var buffer = new CircularBuffer(Array, 3);
+
+    buffer.unshift(1);
+    buffer.unshift(2);
+    buffer.unshift(3);
+    buffer.unshift(4);
+
+    assert.deepEqual(buffer.toArray(), [4, 3, 2]);
+    assert.strictEqual(buffer.size, 3);
+
+    buffer.unshift(5);
+
+    assert.deepEqual(buffer.toArray(), [5, 4, 3]);
+    assert.strictEqual(buffer.size, 3);
+
+    buffer.unshift(6);
+
+    assert.deepEqual(buffer.toArray(), [6, 5, 4]);
+    assert.strictEqual(buffer.size, 3);
+
+    buffer.unshift(7);
+    buffer.unshift(8);
+
+    assert.deepEqual(buffer.toArray(), [8, 7, 6]);
+    assert.strictEqual(buffer.size, 3);
+  });
+
   it('should be possible to clear the buffer.', function() {
     var buffer = new CircularBuffer(Array, 2);
 

test/fixed-deque.js

@@ -43,6 +43,10 @@ describe('FixedDeque', function() {
     assert.throws(function() {
       deque.push('test');
     }, /exceed/);
+
+    assert.throws(function() {
+      deque.unshift('test');
+    }, /exceed/);
   });
 
   it('should be possible to clear the deque.', function() {