messageformat-number-skeleton/lib/pattern-parser/number-tokens.js

A parser & formatter for ICU NumberFormat skeleton strings & patterns

const isDigit = (char) => char >= '0' && char <= '9';
export function parseNumberToken(src, pos) {
    const char = src[pos];
    if (isDigit(char)) {
        let digits = char;
        while (true) {
            const next = src[++pos];
            if (isDigit(next))
                digits += next;
            else
                return { char: '0', digits, width: digits.length };
        }
    }
    switch (char) {
        case '#': {
            let width = 1;
            while (src[++pos] === '#')
                ++width;
            return { char, width };
        }
        case '@': {
            let min = 1;
            while (src[++pos] === '@')
                ++min;
            let width = min;
            pos -= 1;
            while (src[++pos] === '#')
                ++width;
            return { char, min, width };
        }
        case 'E': {
            const plus = src[pos + 1] === '+';
            if (plus)
                ++pos;
            let expDigits = 0;
            while (src[++pos] === '0')
                ++expDigits;
            const width = (plus ? 2 : 1) + expDigits;
            if (expDigits)
                return { char, expDigits, plus, width };
            else
                break;
        }
        case '.':
        case ',':
            return { char, width: 1 };
    }
    return null;
}