add examples about using splice to add elements to array (#31705)

* add examples about using splice to add elements to array

* remove insertion duplication

* Remove word duplication

* move and enhance unshift and push examples

* adhere linting rules

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

* enhance example header

* Apply suggestions from code review

* Update index.md

* Update index.md

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Joshua Chen <[email protected]>

files/en-us/web/javascript/reference/global_objects/array/splice/index.md

@@ -87,6 +87,30 @@ const removed = myFish.splice(2, 0, "drum", "guitar");
 // removed is [], no elements removed
 ```
 
+### Remove 0 (zero) elements at index 0, and insert "angel"
+
+`splice(0, 0, ...elements)` inserts elements at the start of the array like {{jsxref("Array/unshift", "unshift()")}}.
+
+```js
+const myFish = ["clown", "mandarin", "sturgeon"];
+const removed = myFish.splice(0, 0, "angel");
+
+// myFish is ["angel", "clown", "mandarin", "sturgeon"]
+// no items removed
+```
+
+### Remove 0 (zero) elements at last index, and insert "sturgeon"
+
+`splice(array.length, 0, ...elements)` inserts elements at the end of the array like {{jsxref("Array/push", "push()")}}.
+
+```js
+const myFish = ["angel", "clown", "mandarin"];
+const removed = myFish.splice(myFish.length, 0, "sturgeon");
+
+// myFish is ["angel", "clown", "mandarin", "sturgeon"]
+// no items removed
+```
+
 ### Remove 1 element at index 3
 
 ```js