Splice by default mutates/changes/updates inputted array in Javascript. For example:

const test = ['angel', 'clown', 'mandarin', 'sturgeon']; test.splice(2, 1, 'first'); console.log(test); > ['angel', 'clown', 'first', 'sturgeon'] 

If you see in above example splice mutates original array.

We can create immutable splice function in Javascript.

Here we go:

function splice(arr, start, deleteCount, ...addItem) { const result = []; if (start > 0) { result.push(...arr.slice(0, start)); } result.push(...addItem); const len = result.length - addItem.length; let count = deleteCount <= 0 ? len : len + deleteCount; if (arr[count]) { result.push(...arr.slice(count)); } return result; } const test = ['angel', 'clown', 'mandarin', 'sturgeon']; console.log(splice(test, 2, 1, 'drum')); > ['angel', 'clown', 'drum', 'sturgeon'] console.log(test) > ['angel', 'clown', 'mandarin', 'sturgeon'] 

test array in above example isn't mutated.

Welcoming suggestions/concerns. Always happy to update article for any use case.

Thank you! Happy experimenting.

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