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Posted on Feb 25, 2021 • Originally published at learn.coderslang.com on Feb 25, 2021

JavaScript Interview Question #23: Array.splice

#beginners #javascript #codenewbie #webdev

How many times can you splice the array in JavaScript? What's the output?

Let’s start with the definition of splice.

The function splice is available in all JavaScript arrays and accepts the variable number of parameters. Here are 4 important things you should know about splice:

The first parameter is called start and represents the index of the first element that will be removed from the array.
The second argument is deleteCount. It determines the number of array elements that will be removed from the array
The third, the fourth argument, and so on, are the new elements that will be added to the array.
The function splice returns the array formed by deleted elements.

Now, we start the array arr with 5 elements [1, 2, 3, 4, 5].

The first splice extracts 2 elements starting from arr[1]. We immediately save them into the splicedArr.

Before the final splice we have the following state:

[ 1, 4, 5 ]  // arr
[ 2, 3 ]     // splicedArr

The second splice once again removes 2 elements from arr starting at arr[1]. This leaves us with a single element — 1.

Then, we apply the destructuring with ... to the splicedArr and add elements 2 and 3 to the initial array arr.

Here’s the code snippet with 2 additional calls to console.log to help you understand the explanation better:

  const arr = [1, 2, 3, 4, 5];
  const splicedArr = arr.splice(1, 2);

  console.log(arr);         // [ 1, 4, 5 ]
  console.log(splicedArr);  // [ 2, 3 ]

  arr.splice(1, 2, ...splicedArr);
  console.log(arr);