add DID toJson function

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@iden3/js-iden3-core",
-  "version": "1.3.1",
+  "version": "1.3.2",
   "description": "Low level API to create and manipulate iden3 Claims.",
   "source": "./src/index.ts",
   "types": "dist/types/index.d.ts",

src/did/did.ts

@@ -91,6 +91,10 @@ export class DID {
     return buff.join('');
   }
 
+  toJSON() {
+    return this.string();
+  }
+
   static parse(s: string): DID {
     const parser = new Parser(s);
 

tests/did.test.ts

@@ -97,6 +97,18 @@ describe('DID tests', () => {
     expect('did:iden3:readonly:tJ93RwaVfE1PEMxd5rpZZuPtLCwbEaDCrNBhAy8HM').toBe(did2.string());
   });
 
+  it('Test DID to JSON', () => {
+    const didStr = 'did:polygonid:linea:sepolia:32232vGknSaJHfCBffnbzHzYYy6FvHDkK9QL4SFAq6';
+    const did = DID.parse(didStr);
+    const field1Val = 'field1';
+    const objWithDid = {
+      field1: field1Val,
+      did
+    };
+    const stringify = JSON.stringify(objWithDid);
+    expect(stringify).toBe(`{"field1":"${field1Val}","did":"${didStr}"}`);
+  });
+
   describe('TestDID_PolygonID_Types', () => {
     const testCases = [
       {