Add getOrCreateInstance method in base-component (#33276)

Co-authored-by: Rohit Sharma <rohit2sharma95@gmail.com>
Co-authored-by: XhmikosR <xhmikosr@gmail.com>

js/tests/unit/scrollspy.spec.js

@@ -684,6 +684,60 @@ describe('ScrollSpy', () => {
     })
   })
 
+  describe('getOrCreateInstance', () => {
+    it('should return scrollspy instance', () => {
+      fixtureEl.innerHTML = '<div></div>'
+
+      const div = fixtureEl.querySelector('div')
+      const scrollspy = new ScrollSpy(div)
+
+      expect(ScrollSpy.getOrCreateInstance(div)).toEqual(scrollspy)
+      expect(ScrollSpy.getInstance(div)).toEqual(ScrollSpy.getOrCreateInstance(div, {}))
+      expect(ScrollSpy.getOrCreateInstance(div)).toBeInstanceOf(ScrollSpy)
+    })
+
+    it('should return new instance when there is no scrollspy instance', () => {
+      fixtureEl.innerHTML = '<div></div>'
+
+      const div = fixtureEl.querySelector('div')
+
+      expect(ScrollSpy.getInstance(div)).toEqual(null)
+      expect(ScrollSpy.getOrCreateInstance(div)).toBeInstanceOf(ScrollSpy)
+    })
+
+    it('should return new instance when there is no scrollspy instance with given configuration', () => {
+      fixtureEl.innerHTML = '<div></div>'
+
+      const div = fixtureEl.querySelector('div')
+
+      expect(ScrollSpy.getInstance(div)).toEqual(null)
+      const scrollspy = ScrollSpy.getOrCreateInstance(div, {
+        offset: 1
+      })
+      expect(scrollspy).toBeInstanceOf(ScrollSpy)
+
+      expect(scrollspy._config.offset).toEqual(1)
+    })
+
+    it('should return the instance when exists without given configuration', () => {
+      fixtureEl.innerHTML = '<div></div>'
+
+      const div = fixtureEl.querySelector('div')
+      const scrollspy = new ScrollSpy(div, {
+        offset: 1
+      })
+      expect(ScrollSpy.getInstance(div)).toEqual(scrollspy)
+
+      const scrollspy2 = ScrollSpy.getOrCreateInstance(div, {
+        offset: 2
+      })
+      expect(scrollspy).toBeInstanceOf(ScrollSpy)
+      expect(scrollspy2).toEqual(scrollspy)
+
+      expect(scrollspy2._config.offset).toEqual(1)
+    })
+  })
+
   describe('event handler', () => {
     it('should create scrollspy on window load event', () => {
       fixtureEl.innerHTML = '<div data-bs-spy="scroll"></div>'