How is this different from List Reverser?

List Reverser replaces the list's order with its reverse; List Mirror keeps the original order and appends a reversed copy after it, so the result is twice as long and reads the same forwards and backwards.

Is the middle item duplicated for an odd-length list?

Yes, the middle item appears twice in the mirrored output, once at the end of the original half and once at the start of the reversed half, since the mirror is a literal list + reverse(list) concatenation, not a palindrome-aware fold.

How is this different from List Inverter?

List Inverter reverses the characters inside each item while keeping item order the same; List Mirror keeps each item's characters intact but appends a reversed copy of the whole item order. They operate on different things: characters vs. item order.

What length is the output?

Exactly double the input's item count, since every original item appears once in the first half and once again (in reverse order) in the second half.

List Mirror Online - Append a Reversed Copy of a List

Overview

Introduction

A palindrome-style list, one that reads the same forwards and backwards, is a fun visual effect and occasionally a genuinely useful structure for symmetric data or test fixtures.

List Mirror builds that structure automatically: your list, followed immediately by the same list reversed.

What Is List Mirror?

A tool that outputs list + reverse(list), doubling the item count and making the combined order read the same in both directions.

It's distinct from List Reverser, which replaces the order in place rather than appending, and from List Inverter, which reverses characters within items rather than item order.

How List Mirror Works

The input is split into items on the resolved separator, a reversed copy of that array is built with Array.prototype.reverse(), and the original items are concatenated with the reversed copy.

The combined, doubled-length list is then rejoined using the same separator and delimiter settings as the input.

When To Use List Mirror

Use it to build symmetric test data or fixtures where a palindrome-shaped sequence is genuinely useful.

It's also a quick way to create a decorative "echo" effect for a list in plain-text notes or presentations.

Often used alongside List Inverter, List Reverser and List Item Indenter.

Features

Advantages

Guarantees a genuinely palindromic item order, verified by simple concatenation logic.
Item content is never altered, characters within each item are untouched, only the overall order is mirrored.
Works with any configured separator, not just newline-delimited lists.

Limitations

The output is always twice the input length, which isn't appropriate if you actually wanted a true palindrome fold (middle item appearing once).
Doesn't deduplicate the repeated middle item on odd-length lists; it appears exactly as the literal concatenation produces it.

Examples

Mirror a three-item list

Input

a
b
c

Output

a
b
c
c
b
a

The original list is followed immediately by the same list reversed; "c" appears twice at the seam.

Mirror a comma list

Input

1,2,3

Output

1, 2, 3, 3, 2, 1

The doubled, mirrored order reads the same forwards and backwards.

Best Practices & Notes

Best Practices

Use List Reverser instead if you just want the order reversed in place, without doubling the list.
Use List Inverter instead if you want each item's characters reversed rather than the item order.

Developer Notes

Implemented as [...items, ...[...items].reverse()], a plain array spread and concatenation, so the original array reference is never mutated and both halves independently reflect the same source order.

List Mirror Use Cases

Generating symmetric palindrome-shaped test fixtures or sample data
Creating a decorative "echo" list effect for plain-text notes or presentations
Demonstrating the difference between reversing order vs. reversing characters

Common Mistakes

Expecting the middle item of an odd-length list to appear only once; it appears twice by design, once at the end of each half.
Confusing this with List Reverser, which replaces rather than appends the reversed order.
Confusing this with List Inverter, which reverses characters inside items rather than the order of items.

Tips

Use List Reverser first if you actually want a reversed-then-mirrored combination for a more complex shape.
Combine with List Skewer for a staircase-then-mirror visual effect.

List Mirror