Add cursor.flatMap

Author: pluma

CHANGELOG.md

@@ -387,6 +387,11 @@ This is a major release and breaks backwards compatibility.
 
 #### Cursor API
 
+- Added `cursor.flatMap` method
+
+  This method behaves similarly to the `Array` method `flatMap` but operates
+  on the cursor directly like `cursor.map` does.
+
 - Added support for `for await` in `ArrayCursor` ([#616](https://github.com/arangodb/arangojs/pull/616))
 
   It is now possible to use `for await` to iterate over each item in a cursor

src/cursor.ts

@@ -250,6 +250,29 @@ export class ArrayCursor<T = any> {
     return result;
   }
 
+  /**
+   * TODO
+   */
+  async flatMap<U = any>(
+    fn: (value: T, index: number, self: ArrayCursor<T>) => U
+  ): Promise<U[]> {
+    let index = 0;
+    let result: any[] = [];
+    while (this._result.length || this.hasMore) {
+      while (this._result.length) {
+        const value = fn(this._result.shift()!, index, this);
+        if (Array.isArray(value)) {
+          result.push(...value);
+        } else {
+          result.push(value);
+        }
+        index++;
+      }
+      if (this.hasMore) await this._more();
+    }
+    return result;
+  }
+
   /**
    * TODO
    */

src/test/08-cursors.ts

@@ -158,6 +158,23 @@ describe("Cursor API", () => {
       expect(results).to.eql(aqlResult.map((value) => value * 2));
     });
   });
+  describe("cursor.flatMap", () => {
+    it("flat-maps all result values over the callback", async () => {
+      const results = await cursor.flatMap((value) => [value, value * 2]);
+      expect(results).to.eql(
+        aqlResult
+          .map((value) => [value, value * 2])
+          .reduce((acc, next) => {
+            acc.push(...next);
+            return acc;
+          }, [] as number[])
+      );
+    });
+    it("doesn't choke on non-arrays", async () => {
+      const results = await cursor.flatMap((value) => value * 2);
+      expect(results).to.eql(aqlResult.map((value) => value * 2));
+    });
+  });
   describe("cursor.reduce", () => {
     it("reduces the result values with the callback", async () => {
       const result = await cursor.reduce((a, b) => a + b);