feat(database): add support for ServerValue.increment (#3561)

Co-authored-by: Mike Diarmid <mike.diarmid@gmail.com

[publish]

packages/database/e2e/DatabaseStatics.e2e.js

@@ -15,7 +15,13 @@
  *
  */
 
+const { PATH, wipe } = require('./helpers');
+
+const TEST_PATH = `${PATH}/statics`;
+
 describe('database.X', () => {
+  after(() => wipe(TEST_PATH));
+
   describe('ServerValue.TIMESTAMP', () => {
     it('returns a valid object', () => {
       const { TIMESTAMP } = firebase.database.ServerValue;
@@ -24,4 +30,36 @@ describe('database.X', () => {
       TIMESTAMP['.sv'].should.eql('timestamp');
     });
   });
+
+  describe('ServerValue.increment', () => {
+    it('returns a valid object', () => {
+      const incrementObject = firebase.database.ServerValue.increment(1);
+      should.equal(Object.keys(incrementObject).length, 1);
+      incrementObject.should.have.property('.sv');
+      incrementObject['.sv'].should.have.property('increment');
+    });
+
+    it('increments on the server', async () => {
+      const ref = firebase.database().ref(`${TEST_PATH}/increment`);
+
+      await ref.set({ increment: 0 });
+
+      const res1 = await ref.once('value');
+      res1.val().increment.should.equal(0);
+
+      await ref.set({ increment: firebase.database.ServerValue.increment(1) });
+
+      const res2 = await ref.once('value');
+      res2.val().increment.should.equal(1);
+    });
+
+    it('increments on the server when no value is present', async () => {
+      const ref = firebase.database().ref(`${TEST_PATH}/increment-empty`);
+
+      await ref.set({ increment: firebase.database.ServerValue.increment(2) });
+
+      const res = await ref.once('value');
+      res.val().increment.should.equal(2);
+    });
+  });
 });

packages/database/lib/DatabaseStatics.js

@@ -20,5 +20,12 @@ export default {
     TIMESTAMP: {
       '.sv': 'timestamp',
     },
+    increment(delta: number) {
+      return {
+        '.sv': {
+          increment: delta,
+        },
+      };
+    },
   },
 };

packages/database/lib/index.d.ts

@@ -73,6 +73,21 @@ export namespace FirebaseDatabaseTypes {
      * ```
      */
     TIMESTAMP: object;
+
+    /**
+     * Returns a placeholder value that can be used to atomically increment the current database value by the provided delta.
+     *
+     * #### Example
+     *
+     * ```js
+     * firebase.database().ref('posts/123').update({
+     *   likes: firebase.database.ServerValue.increment(1),
+     * });
+     * ```
+     *
+     * @param delta The amount to modify the current value atomically.
+     */
+    increment(delta: number): object;
   }
 
   /**