diff --git a/packages/mermaid/src/assignWithDepth.js b/packages/mermaid/src/assignWithDepth.js
index 6f2e706ab..54302103b 100644
--- a/packages/mermaid/src/assignWithDepth.js
+++ b/packages/mermaid/src/assignWithDepth.js
@@ -20,7 +20,7 @@
  *   of src to dst in order.
  * @param {any} dst - The destination of the merge
  * @param {any} src - The source object(s) to merge into destination
- * @param {{ depth: number; clobber: boolean }} [config] - Depth: depth
+ * @param {{ depth: number; clobber?: boolean }} [config] - Depth: depth
  *   to traverse within src and dst for merging - clobber: should dissimilar types clobber (default:
  *   { depth: 2, clobber: false }). Default is `{ depth: 2, clobber: false }`
  * @returns {any}
diff --git a/packages/mermaid/src/utils.spec.ts b/packages/mermaid/src/utils.spec.ts
index ae3234cb9..271dc588c 100644
--- a/packages/mermaid/src/utils.spec.ts
+++ b/packages/mermaid/src/utils.spec.ts
@@ -1,5 +1,5 @@
 import { vi } from 'vitest';
-import utils from './utils.js';
+import utils, { cleanAndMerge } from './utils.js';
 import assignWithDepth from './assignWithDepth.js';
 import { detectType } from './diagram-api/detectType.js';
 import { addDiagrams } from './diagram-api/diagram-orchestration.js';
@@ -10,51 +10,51 @@ addDiagrams();
 
 describe('when assignWithDepth: should merge objects within objects', function () {
   it('should handle simple, depth:1 types (identity)', function () {
-    let config_0 = { foo: 'bar', bar: 0 };
-    let config_1 = { foo: 'bar', bar: 0 };
-    let result = assignWithDepth(config_0, config_1);
+    const config_0 = { foo: 'bar', bar: 0 };
+    const config_1 = { foo: 'bar', bar: 0 };
+    const result = assignWithDepth(config_0, config_1);
     expect(result).toEqual(config_1);
   });
   it('should handle simple, depth:1 types (dst: undefined)', function () {
-    let config_0 = undefined;
-    let config_1 = { foo: 'bar', bar: 0 };
-    let result = assignWithDepth(config_0, config_1);
+    const config_0 = undefined;
+    const config_1 = { foo: 'bar', bar: 0 };
+    const result = assignWithDepth(config_0, config_1);
     expect(result).toEqual(config_1);
   });
   it('should handle simple, depth:1 types (src: undefined)', function () {
-    let config_0 = { foo: 'bar', bar: 0 };
-    let config_1 = undefined;
-    let result = assignWithDepth(config_0, config_1);
+    const config_0 = { foo: 'bar', bar: 0 };
+    const config_1 = undefined;
+    const result = assignWithDepth(config_0, config_1);
     expect(result).toEqual(config_0);
   });
   it('should handle simple, depth:1 types (merge)', function () {
-    let config_0 = { foo: 'bar', bar: 0 };
-    let config_1 = { foo: 'foo' };
-    let result = assignWithDepth(config_0, config_1);
+    const config_0 = { foo: 'bar', bar: 0 };
+    const config_1 = { foo: 'foo' };
+    const result = assignWithDepth(config_0, config_1);
     expect(result).toEqual({ foo: 'foo', bar: 0 });
   });
   it('should handle depth:2 types (dst: orphan)', function () {
-    let config_0 = { foo: 'bar', bar: { foo: 'bar' } };
-    let config_1 = { foo: 'bar' };
-    let result = assignWithDepth(config_0, config_1);
+    const config_0 = { foo: 'bar', bar: { foo: 'bar' } };
+    const config_1 = { foo: 'bar' };
+    const result = assignWithDepth(config_0, config_1);
     expect(result).toEqual(config_0);
   });
   it('should handle depth:2 types (dst: object, src: simple type)', function () {
-    let config_0 = { foo: 'bar', bar: { foo: 'bar' } };
-    let config_1 = { foo: 'foo', bar: 'should NOT clobber' };
-    let result = assignWithDepth(config_0, config_1);
+    const config_0 = { foo: 'bar', bar: { foo: 'bar' } };
+    const config_1 = { foo: 'foo', bar: 'should NOT clobber' };
+    const result = assignWithDepth(config_0, config_1);
     expect(result).toEqual({ foo: 'foo', bar: { foo: 'bar' } });
   });
   it('should handle depth:2 types (src: orphan)', function () {
-    let config_0 = { foo: 'bar' };
-    let config_1 = { foo: 'bar', bar: { foo: 'bar' } };
-    let result = assignWithDepth(config_0, config_1);
+    const config_0 = { foo: 'bar' };
+    const config_1 = { foo: 'bar', bar: { foo: 'bar' } };
+    const result = assignWithDepth(config_0, config_1);
     expect(result).toEqual(config_1);
   });
   it('should handle depth:2 types (merge)', function () {
-    let config_0 = { foo: 'bar', bar: { foo: 'bar' }, boofar: 1 };
-    let config_1 = { foo: 'foo', bar: { bar: 0 }, foobar: 'foobar' };
-    let result = assignWithDepth(config_0, config_1);
+    const config_0 = { foo: 'bar', bar: { foo: 'bar' }, boofar: 1 };
+    const config_1 = { foo: 'foo', bar: { bar: 0 }, foobar: 'foobar' };
+    const result = assignWithDepth(config_0, config_1);
     expect(result).toEqual({
       foo: 'foo',
       bar: { foo: 'bar', bar: 0 },
@@ -63,17 +63,17 @@ describe('when assignWithDepth: should merge objects within objects', function (
     });
   });
   it('should handle depth:3 types (merge with clobber because assignWithDepth::depth == 2)', function () {
-    let config_0 = {
+    const config_0 = {
       foo: 'bar',
       bar: { foo: 'bar', bar: { foo: { message: 'this', willbe: 'clobbered' } } },
       boofar: 1,
     };
-    let config_1 = {
+    const config_1 = {
       foo: 'foo',
       bar: { foo: 'foo', bar: { foo: { message: 'clobbered other foo' } } },
       foobar: 'foobar',
     };
-    let result = assignWithDepth(config_0, config_1);
+    const result = assignWithDepth(config_0, config_1);
     expect(result).toEqual({
       foo: 'foo',
       bar: { foo: 'foo', bar: { foo: { message: 'clobbered other foo' } } },
@@ -82,7 +82,7 @@ describe('when assignWithDepth: should merge objects within objects', function (
     });
   });
   it('should handle depth:3 types (merge with clobber because assignWithDepth::depth == 1)', function () {
-    let config_0 = {
+    const config_0 = {
       foo: 'bar',
       bar: {
         foo: 'bar',
@@ -90,12 +90,12 @@ describe('when assignWithDepth: should merge objects within objects', function (
       },
       boofar: 1,
     };
-    let config_1 = {
+    const config_1 = {
       foo: 'foo',
       bar: { foo: 'foo', bar: { foo: { message: 'this' } } },
       foobar: 'foobar',
     };
-    let result = assignWithDepth(config_0, config_1, { depth: 1 });
+    const result = assignWithDepth(config_0, config_1, { depth: 1 });
     expect(result).toEqual({
       foo: 'foo',
       bar: { foo: 'foo', bar: { foo: { message: 'this' } } },
@@ -104,17 +104,17 @@ describe('when assignWithDepth: should merge objects within objects', function (
     });
   });
   it('should handle depth:3 types (merge with no clobber because assignWithDepth::depth == 3)', function () {
-    let config_0 = {
+    const config_0 = {
       foo: 'bar',
       bar: { foo: 'bar', bar: { foo: { message: '', willbe: 'present' } } },
       boofar: 1,
     };
-    let config_1 = {
+    const config_1 = {
       foo: 'foo',
       bar: { foo: 'foo', bar: { foo: { message: 'this' } } },
       foobar: 'foobar',
     };
-    let result = assignWithDepth(config_0, config_1, { depth: 3 });
+    const result = assignWithDepth(config_0, config_1, { depth: 3 });
     expect(result).toEqual({
       foo: 'foo',
       bar: { foo: 'foo', bar: { foo: { message: 'this', willbe: 'present' } } },
@@ -125,8 +125,8 @@ describe('when assignWithDepth: should merge objects within objects', function (
 });
 describe('when memoizing', function () {
   it('should return the same value', function () {
-    const fib = memoize(
-      function (n, x, canary) {
+    const fib: any = memoize(
+      function (n: number, x: string, canary: { flag: boolean }) {
         canary.flag = true;
         if (n < 2) {
           return 1;
@@ -260,7 +260,7 @@ describe('when formatting urls', function () {
   it('should handle links', function () {
     const url = 'https://mermaid-js.github.io/mermaid/#/';
 
-    let config = { securityLevel: 'loose' };
+    const config = { securityLevel: 'loose' };
     let result = utils.formatUrl(url, config);
     expect(result).toEqual(url);
 
@@ -271,7 +271,7 @@ describe('when formatting urls', function () {
   it('should handle anchors', function () {
     const url = '#interaction';
 
-    let config = { securityLevel: 'loose' };
+    const config = { securityLevel: 'loose' };
     let result = utils.formatUrl(url, config);
     expect(result).toEqual(url);
 
@@ -282,7 +282,7 @@ describe('when formatting urls', function () {
   it('should handle mailto', function () {
     const url = 'mailto:user@user.user';
 
-    let config = { securityLevel: 'loose' };
+    const config = { securityLevel: 'loose' };
     let result = utils.formatUrl(url, config);
     expect(result).toEqual(url);
 
@@ -293,7 +293,7 @@ describe('when formatting urls', function () {
   it('should handle other protocols', function () {
     const url = 'notes://do-your-thing/id';
 
-    let config = { securityLevel: 'loose' };
+    const config = { securityLevel: 'loose' };
     let result = utils.formatUrl(url, config);
     expect(result).toEqual(url);
 
@@ -304,7 +304,7 @@ describe('when formatting urls', function () {
   it('should handle scripts', function () {
     const url = 'javascript:alert("test")';
 
-    let config = { securityLevel: 'loose' };
+    const config = { securityLevel: 'loose' };
     let result = utils.formatUrl(url, config);
     expect(result).toEqual(url);
 
@@ -425,6 +425,42 @@ describe('when parsing font sizes', function () {
   });
 
   it('handles unparseable input', function () {
+    // @ts-expect-error Explicitly testing unparsable input
     expect(utils.parseFontSize({ fontSize: 14 })).toEqual([undefined, undefined]);
   });
 });
+
+describe('cleanAndMerge', () => {
+  test('should merge objects', () => {
+    expect(cleanAndMerge({ a: 1, b: 2 }, { b: 3 })).toEqual({ a: 1, b: 3 });
+    expect(cleanAndMerge({ a: 1 }, { a: 2 })).toEqual({ a: 2 });
+  });
+
+  test('should remove undefined values', () => {
+    expect(cleanAndMerge({ a: 1, b: 2 }, { b: undefined })).toEqual({ a: 1, b: 2 });
+    expect(cleanAndMerge({ a: 1, b: 2 }, { a: 2, b: undefined })).toEqual({ a: 2, b: 2 });
+    expect(cleanAndMerge({ a: 1, b: { c: 2 } }, { a: 2, b: undefined })).toEqual({
+      a: 2,
+      b: { c: 2 },
+    });
+    // @ts-expect-error Explicitly testing different type
+    expect(cleanAndMerge({ a: 1, b: { c: 2 } }, { a: 2, b: { c: undefined } })).toEqual({
+      a: 2,
+      b: { c: 2 },
+    });
+  });
+
+  test('should create deep copies of object', () => {
+    const input: { a: number; b?: number } = { a: 1 };
+    const output = cleanAndMerge(input, { b: 2 });
+    expect(output).toEqual({ a: 1, b: 2 });
+    output.b = 3;
+    expect(input).toEqual({ a: 1 });
+
+    const inputDeep = { a: { b: 1 } };
+    const outputDeep = cleanAndMerge(inputDeep, { a: { b: 2 } });
+    expect(outputDeep).toEqual({ a: { b: 2 } });
+    outputDeep.a.b = 3;
+    expect(inputDeep).toEqual({ a: { b: 1 } });
+  });
+});
diff --git a/packages/mermaid/src/utils.ts b/packages/mermaid/src/utils.ts
index e48b49fcd..937f3f8f8 100644
--- a/packages/mermaid/src/utils.ts
+++ b/packages/mermaid/src/utils.ts
@@ -31,6 +31,7 @@ import { detectType } from './diagram-api/detectType.js';
 import assignWithDepth from './assignWithDepth.js';
 import { MermaidConfig } from './config.type.js';
 import memoize from 'lodash-es/memoize.js';
+import merge from 'lodash-es/merge.js';
 
 export const ZERO_WIDTH_SPACE = '\u200b';
 
@@ -802,7 +803,7 @@ export const calculateTextDimensions: (
 );
 
 export const initIdGenerator = class iterator {
-  constructor(deterministic, seed) {
+  constructor(deterministic, seed?: any) {
     this.deterministic = deterministic;
     // TODO: Seed is only used for length?
     this.seed = seed;
@@ -994,12 +995,17 @@ export const parseFontSize = (fontSize: string | number | undefined): [number?,
   }
 };
 
+export function cleanAndMerge<T>(defaultData: T, data?: Partial<T>): T {
+  return merge({}, defaultData, data);
+}
+
 export default {
   assignWithDepth,
   wrapLabel,
   calculateTextHeight,
   calculateTextWidth,
   calculateTextDimensions,
+  cleanAndMerge,
   detectInit,
   detectDirective,
   isSubstringInArray,