diff --git a/js/noms/src/specs-test.js b/js/noms/src/specs-test.js
index 8bb54091e2..9f87a4699b 100644
--- a/js/noms/src/specs-test.js
+++ b/js/noms/src/specs-test.js
@@ -6,6 +6,7 @@
 
 import {assert} from 'chai';
 import {suite, test} from 'mocha';
+import {invariant} from './assert.js';
 import {getHash} from './get-hash.js';
 import List from './list.js';
 import {DatabaseSpec, DatasetSpec, PathSpec} from './specs.js';
@@ -100,6 +101,7 @@ suite('Specs', () => {
       const spec = DatabaseSpec.parse(tc.spec);
       assert.strictEqual(spec.scheme, tc.scheme);
       assert.strictEqual(spec.path, tc.path);
+      assert.strictEqual(tc.spec, spec.toString());
     }
   });
 
@@ -154,6 +156,7 @@ suite('Specs', () => {
       assert.strictEqual(tc.scheme, scheme);
       assert.strictEqual(tc.path, path);
       assert.strictEqual(tc.name, spec.name);
+      assert.strictEqual(tc.spec, spec.toString());
     }
   });
 
@@ -189,6 +192,34 @@ suite('Specs', () => {
       assert.strictEqual(tc.scheme, scheme);
       assert.strictEqual(tc.dbPath, path);
       assert.strictEqual(tc.pathStr, spec.path.toString());
+      assert.strictEqual(tc.spec, spec.toString());
     }
   });
+
+
+  test('PathSpec.pin', async () => {
+    const dbSpec = DatabaseSpec.parse('mem');
+    const db = dbSpec.database();
+
+    let ds = db.getDataset('foo');
+    ds = await db.commit(ds, 42);
+
+    const unpinned = PathSpec.parse('mem::foo.value');
+    unpinned.database = dbSpec;
+
+    const pinned = await unpinned.pin();
+    invariant(pinned);
+    const pinnedHash = pinned.path.hash;
+    invariant(pinnedHash);
+    const h = await ds.head();
+    invariant(h);
+    assert.strictEqual(h.hash.toString(), pinnedHash.toString());
+    assert.strictEqual(`mem::#${h.hash.toString()}.value`, pinned.toString());
+    assert.strictEqual(42, (await pinned.value())[1]);
+    assert.strictEqual(42, (await unpinned.value())[1]);
+
+    ds = await db.commit(ds, 43);
+    assert.strictEqual(42, (await pinned.value())[1]);
+    assert.strictEqual(43, (await unpinned.value())[1]);
+  });
 });
diff --git a/js/noms/src/specs.js b/js/noms/src/specs.js
index 16e0c24bce..4a686950b3 100644
--- a/js/noms/src/specs.js
+++ b/js/noms/src/specs.js
@@ -85,6 +85,18 @@ export class DatabaseSpec {
         throw new Error('Unreached');
     }
   }
+
+  toString(): string {
+    switch (this.scheme) {
+      case 'mem':
+        return this.scheme;
+      case 'http':
+      case 'https':
+        return `${this.scheme}:${this.path}`;
+      default:
+        throw new Error('Unreached');
+    }
+  }
 }
 
 /**
@@ -131,6 +143,10 @@ export class DatasetSpec {
     const [db, ds] = this.dataset();
     return ds.head().then(commit => [db, commit ? commit.value : null]);
   }
+
+  toString(): string {
+    return `${this.database.toString()}::${this.name}`;
+  }
 }
 
 /**
@@ -157,6 +173,23 @@ export class PathSpec {
     this.path = path;
   }
 
+  /**
+   * Returns a new PathSpec in which the dataset component, if any, has been
+   * replaced with the hash of the HEAD of that dataset. This "pins" the path
+   * to the state of the database at the current moment in time.
+   */
+  async pin(): Promise<?PathSpec> {
+    if (this.path.dataset !== '') {
+      const ds = this.database.database().getDataset(this.path.dataset);
+      const commit = await ds.head();
+      if (!commit) {
+        return null;
+      }
+      return new PathSpec(this.database,
+        new AbsolutePath('', commit.hash, this.path.path));
+    }
+  }
+
   /**
    * Resolves this PathSpec, and returns the database it was resolved in, and the value it
    * resolved to. If the value wasn't found, it will be `null`.
@@ -167,6 +200,10 @@ export class PathSpec {
     const db = this.database.database();
     return this.path.resolve(db).then(value => [db, value]);
   }
+
+  toString(): string {
+    return `${this.database.toString()}::${this.path.toString()}`;
+  }
 }
 
 function splitAndParseDatabaseSpec(str: string): [DatabaseSpec, string] {
diff --git a/samples/js/fb/find-photos/src/main.js b/samples/js/fb/find-photos/src/main.js
index 6f3a3a1844..2675a8cb4c 100644
--- a/samples/js/fb/find-photos/src/main.js
+++ b/samples/js/fb/find-photos/src/main.js
@@ -8,6 +8,7 @@ import argv from 'yargs';
 import {
   createStructClass,
   DatasetSpec,
+  PathSpec,
   isSubtype,
   makeListType,
   makeStructType,
@@ -23,7 +24,7 @@ import {
 const args = argv
   .usage(
     'Finds photos in slurped Facebook metadata\n\n' +
-    'Usage: node . <in-dataset> <out-dataset>')
+    'Usage: node . <in-path> <out-dataset>')
   .demand(2)
   .argv;
 
@@ -69,10 +70,14 @@ const NomsDate = createStructClass(
   makeStructType('Date', {nsSinceEpoch: numberType}));
 
 async function main(): Promise<void> {
-  const inSpec = DatasetSpec.parse(args._[0]);
-  const [db, input] = await inSpec.value();
+  const inSpec = PathSpec.parse(args._[0]);
+  const pinnedSpec = await inSpec.pin();
+  if (!pinnedSpec) {
+    throw `Invalid input dataset: ${inSpec.path.dataset}`;
+  }
+  const [db, input] = await pinnedSpec.value();
   if (!input) {
-    return db.close();
+    throw `Invalid input spec: ${inSpec.toString()}`;
   }
   const outSpec = DatasetSpec.parse(args._[1]);
   const [outDB, output] = outSpec.dataset();
@@ -99,9 +104,14 @@ async function main(): Promise<void> {
     }
   });
 
-  return outDB.commit(output, await result)
-    .then(() => db.close())
-    .then(() => outDB.close());
+  return outDB.commit(output, await result, {
+    meta: newStruct('', {
+      date: new Date().toISOString(),
+      input: pinnedSpec.toString(),
+    }),
+  })
+  .then(() => db.close())
+  .then(() => outDB.close());
 }
 
 function getGeo(input): Struct {
diff --git a/samples/js/fb/slurp/src/main.js b/samples/js/fb/slurp/src/main.js
index 7e6e71ab51..846309f57d 100644
--- a/samples/js/fb/slurp/src/main.js
+++ b/samples/js/fb/slurp/src/main.js
@@ -104,7 +104,14 @@ async function main(): Promise<void> {
     getPhotos(),
     // TODO: Add more object types here
   ]);
-  await db.commit(out, newStruct('', {user, photos}));
+  await db.commit(out, newStruct('', {
+    user,
+    photos,
+  }), {
+    meta: newStruct('', {
+      date: new Date().toISOString(),
+    }),
+  });
   process.stdout.write(clearLine);
   return;
 }
diff --git a/samples/js/flickr/find-photos/src/main.js b/samples/js/flickr/find-photos/src/main.js
index 99badc6a74..98d3bf7a59 100644
--- a/samples/js/flickr/find-photos/src/main.js
+++ b/samples/js/flickr/find-photos/src/main.js
@@ -7,6 +7,7 @@
 import argv from 'yargs';
 import {
   DatasetSpec,
+  PathSpec,
   getTypeOfValue,
   isSubtype,
   makeStructType,
@@ -76,10 +77,14 @@ main().catch(ex => {
 });
 
 async function main(): Promise<void> {
-  const inSpec = DatasetSpec.parse(args._[0]);
-  const [db, input] = await inSpec.value();
+  const inSpec = PathSpec.parse(args._[0]);
+  const pinnedSpec = await inSpec.pin();
+  if (!pinnedSpec) {
+    throw `Input dataset ${inSpec.path.dataset} does not exist`;
+  }
+  const [db, input] = await pinnedSpec.value();
   if (!input) {
-    return db.close();
+    throw `Input spec ${args._[0]} does not exist`;
   }
   const outSpec = DatasetSpec.parse(args._[1]);
   const [outDB, output] = outSpec.dataset();
@@ -112,9 +117,14 @@ async function main(): Promise<void> {
     return false;
   });
 
-  return outDB.commit(output, await result)
-    .then(() => db.close())
-    .then(() => outDB.close());
+  return outDB.commit(output, await result, {
+    meta: newStruct('', {
+      data: new Date().toISOString(),
+      input: pinnedSpec.toString(),
+    }),
+  })
+  .then(() => db.close())
+  .then(() => outDB.close());
 }
 
 function getGeo(input: Object): Struct {
diff --git a/samples/js/flickr/slurp/src/main.js b/samples/js/flickr/slurp/src/main.js
index 07d79952fa..1f62885f22 100644
--- a/samples/js/flickr/slurp/src/main.js
+++ b/samples/js/flickr/slurp/src/main.js
@@ -86,7 +86,10 @@ async function main(): Promise<void> {
   return db.commit(out, newStruct('', {
     photosetsMeta: jsonToNoms(photosetsJSON),
     photosets: await photosets,
-  })).then(() => db.close());
+  }), {
+    meta: newStruct('', {date: new Date().toISOString()}),
+  })
+  .then(() => db.close());
 }
 
 async function getPhotosetsJSON(): Promise<any> {