wcwidth-o1

Wcwidth-O1

A TypeScript/JavaScript implementation of glibc’s wcwidth(3) and wcswidth(3), optimized to O(1).
Conforms to POSIX.1-2008 (IEEE Std 1003.1) for terminal column width calculation.

Superior Performance

• ⚡️ Instant O(1) lookup time
• 🌏 Full Unicode 17.0 coverage

References:

• OpenGroup wcwidth()
• OpenGroup wcswidth()

Getting Started

Install Wcwidth-O1 via npm:

npm i wcwidth-o1

Usage

JavaScript / TypeScript:

import wcwidth from 'wcwidth-o1';

const example1 = wcwidth('a'); // 1
const example2 = wcwidth('好'); // 2
const example3 = wcwidth('😊'); // 2

or

import { wcwidth, wcswidth } from 'wcwidth-o1';

const example = wcwidth('a'); // 1

const example1 = wcswidth('hi'); // 2
const example2 = wcswidth('안녕하세요'); // 10
const example3 = wcswidth('😊こんにちは'); // 12

Function Parameters:

wcwidth():

• char: A single-character string to measure.

wcswidth():

• str: Input string to evaluate.
• n: Max characters to process (defaults to full length).

Updating Lookup Table

When a new Unicode version is released, the lookup table must be regenerated to follow the latest character width definitions.

1. Prerequisites

• glibc-based Linux distro (e.g. Debian).

2. Generate new lookup table

./genTable.sh

If your environment is not glibc-based, you'll see:

[ WARNING ] Please compile on a glibc-based Linux distro (e.g. Debian).

Once the generation is complete, you should see:

[ SUCCESS ] table.ts generated successfully.

3. Replace files

Copy the generated table.ts into src/:

cp table.ts src/

The lookup table update is then complete.

Behind Wcwidth

In fixed-width terminals, most Latin characters take up one column, while East Asian (CJK) ideographs usually take up two. The challenge is deciding how many “cells” each Unicode character should occupy so that text aligns correctly.

The Unicode standard defines width classes:

• Wide (W) and Fullwidth (F) - always 2 columns
• Halfwidth (H) and Narrow (Na) - always 1 column
• Ambiguous (A) - 1 column normally, but 2 in CJK compatibility mode
• Neutral (N) - treated as 1 column here for simplicity

Other rules include:

• U+0000 (null) - width 0
• Control characters - -1
• Combining marks - width 0
• Soft hyphen (U+00AD) - width 1
• Zero width space (U+200B) - width 0

This logic originates from Markus Kuhn’s reference implementation and is widely used in terminal emulators to ensure consistent alignment.

See Unicode TR#11 for more details.

Feedback

Found something odd?
Feel free to open an issue.

Acknowledgments

• Original wcwidth and wcswidth specifications defined by POSIX.1-2008 (IEEE Std 1003.1).
• Behavior and results are derived from the GNU glibc implementation.
• Historical reference: Markus Kuhn’s wcwidth.c, which inspired most Unicode width logic used today.

License

Distributed under the MIT License.
See LICENSE for more information.