javascript why does value splice code example

Example 1: splice method js

let myFish = ['angel', 'clown', 'mandarin', 'sturgeon']
//insert new element into array at index 2
let removed = myFish.splice(2, 0, 'drum')

// myFish is ["angel", "clown", "drum", "mandarin", "sturgeon"] 
// removed is [], no elements removed

Example 2: remove element from array javascript

let numbers = [1,2,3,4]

// to remove last element
let last_num = numbers.pop();
// numbers will now be [1,2,3]

// to remove first element
let first_num = numbers.shift();
//numbers will now be [2,3]

// to remove at an index
let number_index = 1
let index_num = numbers.splice(number_index,1); //removes 1 element at index 1
//numbers will now be [2]

//these methods will modify the numbers array and return the removed element