perf: speed up member list function (#867)

Previously, `MemberApi.prototype.getMany` would iterate through
`allDeviceInfo` for every role.

Now, it only iterates through `allDeviceInfo` once.

Author: EvanHahn

src/lib/key-by.js

@@ -0,0 +1,24 @@
+/**
+ * Like [`Map.groupBy`][0], but the result's values aren't arrays.
+ *
+ * If multiple values resolve to the same key, an error is thrown.
+ *
+ * [0]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map/groupBy
+ *
+ * @template T
+ * @template K
+ * @param {Iterable<T>} items
+ * @param {(item: T) => K} callbackFn
+ * @returns {Map<K, T>}
+ */
+export function keyBy(items, callbackFn) {
+  /** @type {Map<K, T>} */ const result = new Map()
+  for (const item of items) {
+    const key = callbackFn(item)
+    if (result.has(key)) {
+      throw new Error(`keyBy found duplicate key ${JSON.stringify(key)}`)
+    }
+    result.set(key, item)
+  }
+  return result
+}

src/member-api.js

@@ -9,6 +9,7 @@ import {
   projectKeyToId,
   projectKeyToProjectInviteId,
 } from './utils.js'
+import { keyBy } from './lib/key-by.js'
 import { abortSignalAny } from './lib/ponyfills.js'
 import timingSafeEqual from './lib/timing-safe-equal.js'
 import { ROLES, isRoleIdForNewInvite } from './roles.js'
@@ -279,6 +280,8 @@ export class MemberApi extends TypedEmitter {
       this.#dataTypes.deviceInfo.getMany(),
     ])
 
+    const deviceInfoByConfigCoreId = keyBy(allDeviceInfo, ({ docId }) => docId)
+
     return Promise.all(
       [...allRoles.entries()].map(async ([deviceId, role]) => {
         /** @type {MemberInfo} */
@@ -290,9 +293,7 @@ export class MemberApi extends TypedEmitter {
             'config'
           )
 
-          const deviceInfo = allDeviceInfo.find(
-            ({ docId }) => docId === configCoreId
-          )
+          const deviceInfo = deviceInfoByConfigCoreId.get(configCoreId)
 
           memberInfo.name = deviceInfo?.name
           memberInfo.deviceType = deviceInfo?.deviceType

tests/lib/key-by.js

@@ -0,0 +1,37 @@
+import assert from 'node:assert/strict'
+import test from 'node:test'
+import { keyBy } from '../../src/lib/key-by.js'
+
+test('returns an empty map if passed an empty iterable', () => {
+  assert.deepEqual(
+    keyBy([], () => {
+      throw new Error('Should not be called')
+    }),
+    new Map()
+  )
+})
+
+test('keys a list of items by a key function', () => {
+  const items = [
+    { id: 1, name: 'foo' },
+    { id: 2, name: 'bar' },
+    { id: 3, name: 'baz' },
+  ]
+  const result = keyBy(items, (item) => item.id)
+  assert.deepEqual(
+    result,
+    new Map([
+      [1, items[0]],
+      [2, items[1]],
+      [3, items[2]],
+    ])
+  )
+})
+
+test('duplicate keys', () => {
+  const items = [
+    { id: 1, name: 'foo' },
+    { id: 1, name: 'bar' },
+  ]
+  assert.throws(() => keyBy(items, (item) => item.id))
+})