Add has property (#33)

Ref: Level/community#142
Category: addition

Author: vweevers

README.md

@@ -98,10 +98,28 @@ Does the database implement `db.snapshot()` and do read methods accept a `snapsh
 | `classic-level` | Not yet            |
 | `memory-level`  | Not yet            |
 | `browser-level` | ❌                  |
+| `many-level`    | TBD                |
 | `rave-level`    | TBD                |
 
 </details>
 
+### `has` (boolean)
+
+Does the database implement `has()` and `hasMany()`? Tracked in [Level/community#142](https://github.com/Level/community/issues/142).
+
+<details>
+<summary>Support matrix</summary>
+
+| Module          | Has     |
+| :-------------- | :------ |
+| `classic-level` | Not yet |
+| `memory-level`  | Not yet |
+| `browser-level` | Not yet |
+| `many-level`    | Not yet |
+| `rave-level`    | Not yet |
+
+</details>
+
 ### `permanence` (boolean)
 
 Does data survive after process (or environment) exit? Typically true. False for [`memory-level`](https://github.com/Level/memory-level).

index.d.ts

@@ -31,6 +31,11 @@ export interface IManifest {
    */
   snapshots: boolean
 
+  /**
+   * Does the database implement `has()` and `hasMany()`?
+   */
+  has: boolean
+
   /**
    * Does data survive after process (or environment) exit?
    */

index.js

@@ -11,6 +11,7 @@ exports.supports = function supports (...manifests) {
     implicitSnapshots,
     explicitSnapshots,
     snapshots: implicitSnapshots,
+    has: manifest.has || false,
     permanence: manifest.permanence || false,
     seek: manifest.seek || false,
     createIfMissing: manifest.createIfMissing || false,