fix: not call destroy on destroyed step

shepherd.js/src/step.ts

@@ -5,7 +5,8 @@ import {
   isElement,
   isHTMLElement,
   isFunction,
-  isUndefined
+  isUndefined,
+  isNull
 } from './utils/type-check.ts';
 import { bindAdvance } from './utils/bind.ts';
 import {
@@ -699,7 +700,7 @@ export class Step extends Evented {
    * @private
    */
   _setupElements() {
-    if (!isUndefined(this.el)) {
+    if (!isUndefined(this.el) && !isNull(this.el)) {
       this.destroy();
     }
 

shepherd.js/src/utils/type-check.ts

@@ -37,3 +37,11 @@ export function isString<T>(value: T | string): value is string {
 export function isUndefined<T>(value: T | undefined): value is undefined {
   return value === undefined;
 }
+
+/**
+ * Checks if `value` is null.
+ * @param value The param to check if it is null
+ */
+export function isNull<T>(value: T | undefined | null): value is null {
+  return value === null;
+}

shepherd.js/test/unit/step.spec.js

@@ -441,6 +441,19 @@ describe('Tour | Step', () => {
       ).toBeTruthy();
     });
 
+    it('not calls destroy on the step if the step was destroyed', () => {
+      const step = new Step(tour, {});
+      let destroyCalled = false;
+      step.el = document.createElement('a');
+      step.destroy();
+      step.destroy = () => (destroyCalled = true);
+      step._setupElements();
+      expect(
+        destroyCalled,
+        '_setupElements method not called destroy if the step was destroyed'
+      ).toBeFalsy();
+    });
+
     it('calls destroy on the tooltip if it already exists', () => {
       const step = new Step(tour, {});
       let destroyCalled = false;