React component to get the unicode flag character for a country code; doesn't work on Windows because the flag symbols are missing there

CountryFlag.jsx

import React from "react"

export default class CountryFlag extends React.PureComponent {
    constructor(props) {
        super(props)

        this.state = {
            countryCode: props.countryCode ? props.countryCode : "???",
            fontSize: props.fontSize ? props.fontSize : 24
        }
    }

    /**
     * @param {String} countryCode
     * @returns {String}
     */
    getFlacCharacter(countryCode) {
        // Source: https://github.com/thekelvinliu/country-code-emoji/blob/master/src/index.js
        const offset = 127397
        if (typeof countryCode !== "string") throw new TypeError("argument must be a string")
        const cc = countryCode.toUpperCase()
        return /^[A-Z]{2}$/.test(cc) ? String.fromCodePoint(...[...cc].map(c => c.charCodeAt() + offset)) : null
    }

    render() {
        const { countryCode, fontSize } = this.state
        const style = {
            fontSize: fontSize
        }

        return <span style={style}>{countryCode == "???" ? "❓" : this.getFlacCharacter(countryCode)}</span>
    }
}