diff --git a/js/encoding/DynamicUint8Array.js b/js/encoding/DynamicUint8Array.js
new file mode 100644
index 0000000..5bf0080
--- /dev/null
+++ b/js/encoding/DynamicUint8Array.js
@@ -0,0 +1,54 @@
+/**
+ * @author: Jeff Thompson
+ * See COPYING for copyright and distribution information.
+ * Encapsulate an Uint8Array and support dynamic reallocation.
+ */
+
+/*
+ * Create a DynamicUint8Array where this.array is a Uint8Array of size length.
+ * If length is not supplied, use a default initial length.
+ * The methods will update this.length.
+ * To access the array, use this.array or call subarray.
+ */
+var DynamicUint8Array = function DynamicUint8Array(length) {
+	if (!length)
+        length = 16;
+    
+    this.array = new Uint8Array(length);
+    this.length = length;
+};
+
+/*
+ * Ensure that this.array has the length, reallocate and copy if necessary.
+ * Update this.length which may be greater than length.
+ */
+DynamicUint8Array.prototype.ensureLength = function(length) {
+    if (this.array.length >= length)
+        return;
+    
+    // See if double is enough.
+    var newLength = this.array.length * 2;
+    if (length > newLength)
+        // The needed length is much greater, so use it.
+        newLength = length;
+    
+    var newArray = new Uint8Array(newLength);
+    newArray.set(this.array);
+    this.array = newArray;
+    this.length = newLength;
+};
+
+/*
+ * Call this.array.set(value, offset), reallocating if necessary. 
+ */
+DynamicUint8Array.prototype.set = function(value, offset) {
+    this.ensureLength(value.length + offset);
+    this.array.set(value, offset);
+};
+
+/*
+ * Return this.array.subarray(begin, end);
+ */
+DynamicUint8Array.prototype.subarray = function(begin, end) {
+    return this.array.subarray(begin, end);
+}