Japanese half-width kana dakuten(ﾞ) and han-dakuten(ﾟ) are not counted.

import stringWidth from 'string-width'
console.log(stringWidth('ﾊﾞ')) // => 1
console.log(stringWidth('ﾊﾟ')) // => 1

Since dakuten(ﾞ) and han-dakuten(ﾟ) actually have width, these results should be 2.