Support promises and abstract-level

Author: vweevers

README.md

@@ -1,6 +1,6 @@
 # level-concat-iterator
 
-> Concatenate items from an iterator into an array.
+> Concatenate entries from an iterator into an array.
 
 [![level badge][level-badge]](https://github.com/Level/awesome)
 [![npm](https://img.shields.io/npm/v/level-concat-iterator.svg?label=&logo=npm)](https://www.npmjs.com/package/level-concat-iterator)
@@ -23,21 +23,29 @@ const db = level('./db')
 db.put('foo', 'bar', function (err) {
   if (err) throw err
 
-  concat(db.iterator(), function (err, data) {
+  concat(db.iterator(), function (err, entries) {
     if (err) throw err
 
-    console.log(data)
+    // [{ key: 'foo', value: 'bar' }]
+    console.log(entries)
   })
 })
 ```
 
+With promises:
+
+```js
+await db.put('foo', 'bar')
+const entries = await concat(db.iterator())
+```
+
 **If you are upgrading:** please see [`UPGRADING.md`](UPGRADING.md).
 
 ## API
 
-### `concat(iterator, cb)`
+### `concat(iterator[, callback])`
 
-Takes an `abstract-leveldown` compatible `iterator` as first parameter and calls back with an array of keys and values. Calls back with an error if `iterator.next(cb)` or `iterator.end(cb)` errors.
+Takes an `abstract-leveldown` compatible `iterator` as first parameter and calls the `callback` with an array of entries, where each entry is an object in the form `{ key, value }`. Calls the `callback` with an error if `iterator.next()` or `iterator.end()` errors. If no callback is provided, a promise is returned.
 
 ## Contributing
 

example.js

@@ -6,9 +6,9 @@ const db = level('./db')
 db.put('foo', 'bar', function (err) {
   if (err) throw err
 
-  concat(db.iterator(), function (err, data) {
+  concat(db.iterator(), function (err, entries) {
     if (err) throw err
 
-    console.log(data)
+    console.log(entries)
   })
 })

index.js

@@ -1,17 +1,25 @@
 'use strict'
 
-module.exports = function (iterator, cb) {
-  const data = []
-  const next = function () {
-    iterator.next(function (err, key, value) {
-      if (err || (key === undefined && value === undefined)) {
-        return iterator.end(function (err2) {
-          cb(err || err2, data)
-        })
-      }
-      data.push({ key, value })
-      next()
-    })
+const { fromCallback } = require('catering')
+const kPromise = Symbol('promise')
+
+module.exports = function (iterator, callback) {
+  callback = fromCallback(callback, kPromise)
+
+  // Use close() method of abstract-level or end() of abstract-leveldown
+  const close = typeof iterator.close === 'function' ? 'close' : 'end'
+  const entries = []
+
+  const onnext = function (err, key, value) {
+    if (err || (key === undefined && value === undefined)) {
+      return iterator[close](function (err2) {
+        callback(err || err2, entries)
+      })
+    }
+    entries.push({ key, value })
+    iterator.next(onnext)
   }
-  next()
+
+  iterator.next(onnext)
+  return callback[kPromise]
 }

package.json

@@ -1,7 +1,7 @@
 {
   "name": "level-concat-iterator",
   "version": "3.0.0",
-  "description": "Concatenate items from an iterator into an array.",
+  "description": "Concatenate entries from an iterator into an array.",
   "author": "Lars-Magnus Skog <ralphtheninja@riseup.net>",
   "license": "MIT",
   "main": "index.js",
@@ -19,6 +19,9 @@
     "LICENSE.md",
     "UPGRADING.md"
   ],
+  "dependencies": {
+    "catering": "^2.1.0"
+  },
   "devDependencies": {
     "airtap": "^4.0.3",
     "airtap-playwright": "^1.0.1",

test.js

@@ -22,6 +22,25 @@ test('calls back with error if iterator.next errors', function (t) {
   })
 })
 
+test('rejects promise if iterator.next errors', function (t) {
+  t.plan(3)
+
+  const iterator = {
+    next (cb) {
+      t.pass('iterator.next called')
+      process.nextTick(cb, new Error('iterator.next'))
+    },
+    end (cb) {
+      t.pass('iterator.end called')
+      process.nextTick(cb)
+    }
+  }
+
+  collect(iterator).catch(function (err) {
+    t.is(err.message, 'iterator.next', 'correct error')
+  })
+})
+
 test('happy path calls back with an array', function (t) {
   t.plan(6)
 
@@ -53,6 +72,34 @@ test('happy path calls back with an array', function (t) {
   })
 })
 
+test('happy path resolves promise with an array', async function (t) {
+  t.plan(5)
+
+  let i = 0
+  const entries = [
+    { key: 'key1', value: 'value1' },
+    { key: 'key2', value: 'value2' }
+  ]
+
+  const iterator = {
+    next (cb) {
+      t.pass('iterator.next called')
+      if (i < entries.length) {
+        process.nextTick(cb, null, entries[i].key, entries[i].value)
+        ++i
+      } else {
+        process.nextTick(cb)
+      }
+    },
+    end (cb) {
+      t.pass('iterator.end called')
+      process.nextTick(cb)
+    }
+  }
+
+  t.same(await collect(iterator), entries)
+})
+
 test('calls back with error and data if iterator.end errors', function (t) {
   t.plan(6)
 
@@ -84,6 +131,25 @@ test('calls back with error and data if iterator.end errors', function (t) {
   })
 })
 
+test('rejects promise if iterator.end errors', function (t) {
+  t.plan(3)
+
+  const iterator = {
+    next (cb) {
+      t.pass('iterator.next called')
+      process.nextTick(cb)
+    },
+    end (cb) {
+      t.pass('iterator.end called')
+      process.nextTick(cb, new Error('iterator.end'))
+    }
+  }
+
+  collect(iterator).catch(function (err) {
+    t.is(err.message, 'iterator.end', 'correct error')
+  })
+})
+
 test('calls back with error and partial data if iterator.end errors', function (t) {
   t.plan(5)
 
@@ -114,3 +180,24 @@ test('calls back with error and partial data if iterator.end errors', function (
     t.same(result, [].concat(data[0]))
   })
 })
+
+test('prefers iterator.close() over iterator.end()', async function (t) {
+  t.plan(2)
+
+  const iterator = {
+    next (cb) {
+      t.pass('iterator.next called')
+      process.nextTick(cb)
+    },
+    close (cb) {
+      t.pass('iterator.close called')
+      process.nextTick(cb)
+    },
+    end (cb) {
+      t.fail('iterator.end called')
+      process.nextTick(cb)
+    }
+  }
+
+  await collect(iterator)
+})