diff --git a/LICENSE.txt b/LICENSE.txt
index 5496b67fd..b9601d34b 100644
--- a/LICENSE.txt
+++ b/LICENSE.txt
@@ -24,3 +24,28 @@ DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+=====
+
+MIT License for codepointat.js from https://git.io/codepointat
+
+Copyright Mathias Bynens <https://mathiasbynens.be/>
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
diff --git a/runtime/JavaScript/src/antlr4/FileStream.js b/runtime/JavaScript/src/antlr4/FileStream.js
index 97c0eb583..ef89fc4a1 100644
--- a/runtime/JavaScript/src/antlr4/FileStream.js
+++ b/runtime/JavaScript/src/antlr4/FileStream.js
@@ -13,9 +13,9 @@ var InputStream = require('./InputStream').InputStream;
 var isNodeJs = typeof window === 'undefined' && typeof importScripts === 'undefined';
 var fs = isNodeJs ? require("fs") : null;
 
-function FileStream(fileName) {
+function FileStream(fileName, decodeToUnicodeCodePoints) {
 	var data = fs.readFileSync(fileName, "utf8");
-	InputStream.call(this, data);
+	InputStream.call(this, data, decodeToUnicodeCodePoints);
 	this.fileName = fileName;
 	return this;
 }
diff --git a/runtime/JavaScript/src/antlr4/InputStream.js b/runtime/JavaScript/src/antlr4/InputStream.js
index 3ed0ba2f1..87950af2b 100644
--- a/runtime/JavaScript/src/antlr4/InputStream.js
+++ b/runtime/JavaScript/src/antlr4/InputStream.js
@@ -6,22 +6,37 @@
 //
 
 var Token = require('./Token').Token;
+require('./polyfills/codepointat');
 
 // Vacuum all input from a string and then treat it like a buffer.
 
-function _loadString(stream) {
+function _loadString(stream, decodeToUnicodeCodePoints) {
 	stream._index = 0;
 	stream.data = [];
-	for (var i = 0; i < stream.strdata.length; i++) {
-		stream.data.push(stream.strdata.charCodeAt(i));
+	if (decodeToUnicodeCodePoints) {
+		for (var i = 0; i < stream.strdata.length; ) {
+			var codePoint = stream.strdata.codePointAt(i);
+			stream.data.push(codePoint);
+			i += codePoint <= 0xFFFF ? 1 : 2;
+		}
+	} else {
+		for (var i = 0; i < stream.strdata.length; i++) {
+			var codeUnit = stream.strdata.charCodeAt(i);
+			stream.data.push(codeUnit);
+		}
 	}
 	stream._size = stream.data.length;
 }
 
-function InputStream(data) {
+// If decodeToUnicodeCodePoints is true, the input is treated
+// as a series of Unicode code points.
+//
+// Otherwise, the input is treated as a series of 16-bit UTF-16 code
+// units.
+function InputStream(data, decodeToUnicodeCodePoints) {
 	this.name = "<empty>";
 	this.strdata = data;
-	_loadString(this);
+	_loadString(this, decodeToUnicodeCodePoints || false);
 	return this;
 }
 
diff --git a/runtime/JavaScript/src/antlr4/index.js b/runtime/JavaScript/src/antlr4/index.js
index 61a090e91..a0e5683b3 100644
--- a/runtime/JavaScript/src/antlr4/index.js
+++ b/runtime/JavaScript/src/antlr4/index.js
@@ -3,6 +3,7 @@
  * can be found in the LICENSE.txt file in the project root.
  */
 exports.atn = require('./atn/index');
+exports.codepointat = require('./polyfills/codepointat');
 exports.dfa = require('./dfa/index');
 exports.tree = require('./tree/index');
 exports.error = require('./error/index');
diff --git a/runtime/JavaScript/src/antlr4/polyfills/codepointat.js b/runtime/JavaScript/src/antlr4/polyfills/codepointat.js
new file mode 100644
index 000000000..f724c8926
--- /dev/null
+++ b/runtime/JavaScript/src/antlr4/polyfills/codepointat.js
@@ -0,0 +1,54 @@
+/*! https://mths.be/codepointat v0.2.0 by @mathias */
+if (!String.prototype.codePointAt) {
+	(function() {
+		'use strict'; // needed to support `apply`/`call` with `undefined`/`null`
+		var defineProperty = (function() {
+			// IE 8 only supports `Object.defineProperty` on DOM elements
+			try {
+				var object = {};
+				var $defineProperty = Object.defineProperty;
+				var result = $defineProperty(object, object, object) && $defineProperty;
+			} catch(error) {}
+			return result;
+		}());
+		var codePointAt = function(position) {
+			if (this == null) {
+				throw TypeError();
+			}
+			var string = String(this);
+			var size = string.length;
+			// `ToInteger`
+			var index = position ? Number(position) : 0;
+			if (index != index) { // better `isNaN`
+				index = 0;
+			}
+			// Account for out-of-bounds indices:
+			if (index < 0 || index >= size) {
+				return undefined;
+			}
+			// Get the first code unit
+			var first = string.charCodeAt(index);
+			var second;
+			if ( // check if it’s the start of a surrogate pair
+				first >= 0xD800 && first <= 0xDBFF && // high surrogate
+				size > index + 1 // there is a next code unit
+			) {
+				second = string.charCodeAt(index + 1);
+				if (second >= 0xDC00 && second <= 0xDFFF) { // low surrogate
+					// https://mathiasbynens.be/notes/javascript-encoding#surrogate-formulae
+					return (first - 0xD800) * 0x400 + second - 0xDC00 + 0x10000;
+				}
+			}
+			return first;
+		};
+		if (defineProperty) {
+			defineProperty(String.prototype, 'codePointAt', {
+				'value': codePointAt,
+				'configurable': true,
+				'writable': true
+			});
+		} else {
+			String.prototype.codePointAt = codePointAt;
+		}
+	}());
+}