Fix floating promise in constructor (closes #656) (#680)

Author: vweevers

README.md

@@ -111,7 +111,7 @@ The main entry point for creating a new `levelup` instance.
 - `db` must be an [`abstract-leveldown`](https://github.com/Level/abstract-leveldown) compliant store.
 - `options` is passed on to the underlying store when opened and is specific to the type of store being used
 
-Calling `levelup(db)` will also open the underlying store. This is an asynchronous operation which will trigger your callback if you provide one. The callback should take the form `function (err, db) {}` where `db` is the `levelup` instance. If you don't provide a callback, any read & write operations are simply queued internally until the store is fully opened.
+Calling `levelup(db)` will also open the underlying store. This is an asynchronous operation which will trigger your callback if you provide one. The callback should take the form `function (err, db) {}` where `db` is the `levelup` instance. If you don't provide a callback, any read & write operations are simply queued internally until the store is fully opened, unless it fails to open, in which case an `error` event will be emitted.
 
 This leads to two alternative ways of managing a `levelup` instance:
 
@@ -487,6 +487,7 @@ const main = async () => {
 | `ready`   | Alias of `open`             | -                    |
 | `closing` | Store is closing            | -                    |
 | `closed`  | Store has closed.           | -                    |
+| `error`   | An error occurred           | `error` (Error)      |
 
 For example you can do:
 

lib/levelup.js

@@ -31,6 +31,7 @@ function LevelUP (db, options, callback) {
   }
 
   var error
+  var self = this
 
   EventEmitter.call(this)
   this.setMaxListeners(Infinity)
@@ -55,7 +56,9 @@ function LevelUP (db, options, callback) {
   this.options = getOptions(options)
   this._db = db
   this.db = new DeferredLevelDOWN(db)
-  this.open(callback)
+  this.open(callback || function (err) {
+    if (err) self.emit('error', err)
+  })
 
   // Create manifest based on deferred-leveldown's
   this.supports = supports(this.db.supports, {

test/init-test.js

@@ -39,6 +39,40 @@ module.exports = function (test, testCommon) {
     })
   })
 
+  test('Init & open(): error with callback', function (t) {
+    t.plan(1)
+
+    var mem = memdown()
+    mem._open = function (opts, cb) {
+      process.nextTick(cb, new Error('from underlying store'))
+    }
+
+    levelup(mem, function (err) {
+      t.is(err.message, 'from underlying store')
+    }).on('open', function () {
+      t.fail('should not finish opening')
+    }).on('error', function () {
+      t.fail('should not emit error')
+    })
+  })
+
+  test('Init & open(): error without callback', function (t) {
+    t.plan(1)
+
+    var mem = memdown()
+    mem._open = function (opts, cb) {
+      process.nextTick(cb, new Error('from underlying store'))
+    }
+
+    levelup(mem)
+      .on('open', function () {
+        t.fail('should not finish opening')
+      })
+      .on('error', function (err) {
+        t.is(err.message, 'from underlying store')
+      })
+  })
+
   test('Init & open(): validate abstract-leveldown', function (t) {
     t.plan(1)