Call toJSON() on non-ext objects when it exists

Author: kevincennis

src/Encoder.ts

@@ -7,6 +7,10 @@ import type { ExtData } from "./ExtData";
 export const DEFAULT_MAX_DEPTH = 100;
 export const DEFAULT_INITIAL_BUFFER_SIZE = 2048;
 
+const hastoJSON = (value: unknown): value is { toJSON: unknown } => {
+  return typeof value === 'object' && value !== null && 'toJSON' in value;
+};
+
 export class Encoder<ContextType = undefined> {
   private pos = 0;
   private view = new DataView(new ArrayBuffer(this.initialBufferSize));
@@ -187,14 +191,19 @@ export class Encoder<ContextType = undefined> {
   private encodeObject(object: unknown, depth: number) {
     // try to encode objects with custom codec first of non-primitives
     const ext = this.extensionCodec.tryToEncode(object, this.context);
+
     if (ext != null) {
       this.encodeExtension(ext);
     } else if (Array.isArray(object)) {
       this.encodeArray(object, depth);
     } else if (ArrayBuffer.isView(object)) {
       this.encodeBinary(object);
     } else if (typeof object === "object") {
-      this.encodeMap(object as Record<string, unknown>, depth);
+      if (hastoJSON(object) && typeof object.toJSON === "function") {
+        this.doEncode(object.toJSON(), depth);
+      } else {
+        this.encodeMap(object as Record<string, unknown>, depth);
+      }
     } else {
       // symbol, function and other special object come here unless extensionCodec handles them.
       throw new Error(`Unrecognized object: ${Object.prototype.toString.apply(object)}`);

test/decodeAsync.test.ts

@@ -120,4 +120,43 @@ describe("decodeAsync", () => {
     const object = await decodeAsync(createStream());
     assert.deepStrictEqual(object, { "foo": "bar" });
   });
+
+  it("decodes objects with toJSON methods", async () => {
+    const object = {
+      string: "Hello, world!",
+      nested: {
+        int: -45,
+        json: {
+          toJSON() {
+            return {
+              float: Math.PI,
+              int64: Number.MIN_SAFE_INTEGER,
+              timestamp: new Date( 0 ),
+              custom: {
+                toJSON: () => "custom"
+              }
+            }
+          }
+        }
+      }
+    };
+
+    const createStream = async function* () {
+      for (const byte of encode(object)) {
+        yield [byte];
+      }
+    };
+    assert.deepStrictEqual(await decodeAsync(createStream()), {
+      string: "Hello, world!",
+      nested: {
+        int: -45,
+        json: {
+          float: Math.PI,
+          int64: Number.MIN_SAFE_INTEGER,
+          timestamp: new Date( 0 ),
+          custom: "custom"
+        }
+      }
+    });
+  });
 });