diff --git a/js/src/main.js b/js/src/main.js
index 57d881c..fd18f2b 100644
--- a/js/src/main.js
+++ b/js/src/main.js
@@ -18,6 +18,7 @@ copyKeys(['__', '_$', '$Capture', '$Special',
 	 module.exports.Route);
 
 module.exports.DemandMatcher = require('./demand-matcher.js').DemandMatcher;
+module.exports.Seal = require('./seal.js').Seal;
 
 // module.exports.DOM = require("./dom-driver.js");
 module.exports.JQuery = require("./jquery-driver.js");
diff --git a/js/src/seal.js b/js/src/seal.js
new file mode 100644
index 0000000..f30c996
--- /dev/null
+++ b/js/src/seal.js
@@ -0,0 +1,10 @@
+function Seal(contents) {
+  this.sealContents = contents;
+}
+
+Seal.prototype.equals = function (other) {
+  if (!(other instanceof Seal)) return false;
+  return Immutable.is(this.sealContents, other.sealContents);
+};
+
+module.exports.Seal = Seal;