diff --git a/implementations/javascript/package.json b/implementations/javascript/package.json
index 73c3453..92c31b7 100644
--- a/implementations/javascript/package.json
+++ b/implementations/javascript/package.json
@@ -1,6 +1,6 @@
 {
   "name": "preserves",
-  "version": "0.0.11",
+  "version": "0.0.12",
   "description": "Experimental data serialization format",
   "homepage": "https://gitlab.com/tonyg/preserves",
   "license": "MIT",
diff --git a/implementations/javascript/src/codec.js b/implementations/javascript/src/codec.js
index c1760da..4c5b054 100644
--- a/implementations/javascript/src/codec.js
+++ b/implementations/javascript/src/codec.js
@@ -1,6 +1,11 @@
 "use strict";
 // Preserves Binary codec.
 
+if (require('./singletonmodule.js')('leastfixedpoint.com/preserves',
+                                    require('../package.json').version,
+                                    'codec.js',
+                                    module)) return;
+
 const Values = require('./values.js');
 const { List, Map, Set, Bytes, Record, Single, Double } = Values;
 
diff --git a/implementations/javascript/src/index.js b/implementations/javascript/src/index.js
index f5ae110..e95d2ca 100644
--- a/implementations/javascript/src/index.js
+++ b/implementations/javascript/src/index.js
@@ -1,5 +1,10 @@
 "use strict";
 
+if (require('./singletonmodule.js')('leastfixedpoint.com/preserves',
+                                    require('../package.json').version,
+                                    'index.js',
+                                    module)) return;
+
 Object.assign(module.exports, require('./symbols.js'));
 Object.assign(module.exports, require('./codec.js'));
 Object.assign(module.exports, require('./values.js'));
diff --git a/implementations/javascript/src/singletonmodule.js b/implementations/javascript/src/singletonmodule.js
new file mode 100644
index 0000000..1fd54c2
--- /dev/null
+++ b/implementations/javascript/src/singletonmodule.js
@@ -0,0 +1,26 @@
+"use strict";
+
+function initialize_singleton(namespace_key_str, package_version, module_key, module_object) {
+  const namespace_key = Symbol.for(namespace_key_str);
+  if (!(namespace_key in global)) {
+    global[namespace_key] = {
+      version: package_version,
+      modules: {}
+    };
+  }
+  let cache = global[namespace_key];
+  if (cache.version !== package_version) {
+    console.warn('Potentially incompatible versions of ' + namespace_key_str + ' loaded:',
+                 cache.version,
+                 package_version);
+  }
+  if (module_key in cache.modules) {
+    module_object.exports = cache.modules[module_key];
+    return true;
+  } else {
+    cache.modules[module_key] = module_object.exports;
+    return false;
+  }
+}
+
+module.exports = initialize_singleton;
diff --git a/implementations/javascript/src/symbols.js b/implementations/javascript/src/symbols.js
index 0b28e47..b0b1e3f 100644
--- a/implementations/javascript/src/symbols.js
+++ b/implementations/javascript/src/symbols.js
@@ -1,6 +1,11 @@
 "use strict";
 // Symbols for various Preserves protocols.
 
+if (require('./singletonmodule.js')('leastfixedpoint.com/preserves',
+                                    require('../package.json').version,
+                                    'symbols.js',
+                                    module)) return;
+
 const PreserveOn = Symbol.for('PreserveOn');
 const AsPreserve = Symbol.for('AsPreserve');
 
diff --git a/implementations/javascript/src/values.js b/implementations/javascript/src/values.js
index a7ff840..809e455 100644
--- a/implementations/javascript/src/values.js
+++ b/implementations/javascript/src/values.js
@@ -2,6 +2,11 @@
 // Preserves Values.
 // Uses Immutable.js for many things; adds immutable values of its own for the rest.
 
+if (require('./singletonmodule.js')('leastfixedpoint.com/preserves',
+                                    require('../package.json').version,
+                                    'values.js',
+                                    module)) return;
+
 const util = require('util');
 
 const Immutable = require('immutable');
diff --git a/implementations/javascript/test/test-singletonmodule.js b/implementations/javascript/test/test-singletonmodule.js
new file mode 100644
index 0000000..82187e1
--- /dev/null
+++ b/implementations/javascript/test/test-singletonmodule.js
@@ -0,0 +1,51 @@
+"use strict";
+// We really, really, REALLY want not to load two separate
+// implementations of values.js into the same node.js instance, so
+// there's a bunch of singleton hackery in values.js. These tests
+// check that separate loads don't cause separate instances.
+
+const chai = require('chai');
+const expect = chai.expect;
+chai.use(require('chai-immutable'));
+
+const Immutable = require('immutable');
+
+describe('reloading values.js', () => {
+  const V1 = require('../src/values.js');
+  delete require.cache[require.resolve('../src/values.js')];
+  const V2 = require('../src/values.js');
+
+  const C1 = V1.Record.makeConstructor('c', ['a', 'b']);
+  const C2 = V2.Record.makeConstructor('c', ['a', 'b']);
+
+  it('should reuse RecordConstructorInfo (1)', () => {
+    expect(C1.constructorInfo instanceof V1.RecordConstructorInfo).to.be.true;
+  });
+  it('should reuse RecordConstructorInfo (2)', () => {
+    expect(C1.constructorInfo instanceof V2.RecordConstructorInfo).to.be.true;
+  });
+  it('should identify RecordConstructorInfo', () => {
+    expect(Object.is(V1.RecordConstructorInfo, V2.RecordConstructorInfo)).to.be.true;
+  });
+  it('should produce identical module instances', () => { expect(V1 === V2).to.be.true; });
+
+  it('should produce distinct constructor instances', () => { expect(C1 === C2).to.be.false; });
+  it('should produce distinct constructor info', () => {
+    expect(Object.is(C1.constructorInfo, C2.constructorInfo)).to.be.false;
+  });
+  it('should produce compatible constructor info', () => {
+    expect(Immutable.is(C1.constructorInfo, C2.constructorInfo)).to.be.true;
+  });
+  it('should produce compatible record instances', () => {
+    expect(Immutable.is(C1(1,2), C2(1,2))).to.be.true;
+  });
+});
+
+describe('reloading index.js', () => {
+  it('produces identical module exports objects', () => {
+    const I1 = require('../src/index.js');
+    delete require.cache[require.resolve('../src/index.js')];
+    const I2 = require('../src/index.js');
+    expect(Object.is(I1, I2)).to.be.true;
+  });
+});