fix(memleak): in watch mode, do not use promise chain

Promise chains are great for things that WILL resolve. If we know that
this will never resolve (like watch) then we should use a simple
callback based approach like queue/async.

This also re-ensures us that every changes are applied sequentially
(while with our previous check it was no more the case).

I hope this just works™

Author: vvo

index.js

@@ -6,6 +6,7 @@ import PouchDB from 'pouchdb-http';
 import * as npm from './npm.js';
 import log from './log.js';
 import ms from 'ms';
+import queue from 'async/queue';
 
 log.info('🗿 npm ↔️ Algolia replication starts ⛷ 🐌 🛰');
 
@@ -168,9 +169,8 @@ function watch({ seq }) {
       limit: undefined,
     });
 
-    changes.on('change', change => {
-      Promise.resolve()
-        .then(() => saveDocs([change]), reject)
+    const q = queue((change, done) => {
+      saveDocs([change])
         .then(() => infoChange(change.seq, 1, '🛰'))
         .then(() =>
           stateManager.save({
@@ -195,7 +195,12 @@ function watch({ seq }) {
               });
           }
         })
-        .catch(reject);
+        .then(() => done(null))
+        .catch(done);
+    }, 1);
+
+    changes.on('change', change => {
+      q.push(change);
     });
     changes.on('error', reject);
   });

package.json

@@ -24,6 +24,7 @@
   "license": "MIT",
   "dependencies": {
     "algoliasearch": "^3.22.1",
+    "async": "^2.4.0",
     "babel-cli": "^6.24.1",
     "babel-preset-env": "^1.4.0",
     "babel-preset-stage-2": "^6.24.1",

yarn.lock

@@ -177,6 +177,12 @@ async-each@^1.0.0:
   version "1.0.1"
   resolved "https://registry.yarnpkg.com/async-each/-/async-each-1.0.1.tgz#19d386a1d9edc6e7c1c85d388aedbcc56d33602d"
 
+async@^2.4.0:
+  version "2.4.0"
+  resolved "https://registry.yarnpkg.com/async/-/async-2.4.0.tgz#4990200f18ea5b837c2cc4f8c031a6985c385611"
+  dependencies:
+    lodash "^4.14.0"
+
 asynckit@^0.4.0:
   version "0.4.0"
   resolved "https://registry.yarnpkg.com/asynckit/-/asynckit-0.4.0.tgz#c79ed97f7f34cb8f2ba1bc9790bcc366474b4b79"
@@ -2581,7 +2587,7 @@ lodash.isnull@^3.0.0:
   version "3.0.0"
   resolved "https://registry.yarnpkg.com/lodash.isnull/-/lodash.isnull-3.0.0.tgz#fafbe59ea1dca27eed786534039dd84c2e07c56e"
 
-lodash@^4.0.0, lodash@^4.17.2, lodash@^4.17.4, lodash@^4.2.0, lodash@^4.3.0:
+lodash@^4.0.0, lodash@^4.14.0, lodash@^4.17.2, lodash@^4.17.4, lodash@^4.2.0, lodash@^4.3.0:
   version "4.17.4"
   resolved "https://registry.yarnpkg.com/lodash/-/lodash-4.17.4.tgz#78203a4d1c328ae1d86dca6460e369b57f4055ae"