entities/src/decode-codepoint.ts

Encode & decode XML and HTML entities with ease & speed

// Adapted from https://github.com/mathiasbynens/he/blob/36afe179392226cf1b6ccdb16ebbb7a5a844d93a/src/he.js#L106-L134

const decodeMap = new Map([
    [0, 65_533],
    // C1 Unicode control character reference replacements
    [128, 8364],
    [130, 8218],
    [131, 402],
    [132, 8222],
    [133, 8230],
    [134, 8224],
    [135, 8225],
    [136, 710],
    [137, 8240],
    [138, 352],
    [139, 8249],
    [140, 338],
    [142, 381],
    [145, 8216],
    [146, 8217],
    [147, 8220],
    [148, 8221],
    [149, 8226],
    [150, 8211],
    [151, 8212],
    [152, 732],
    [153, 8482],
    [154, 353],
    [155, 8250],
    [156, 339],
    [158, 382],
    [159, 376],
]);

/**
 * Polyfill for `String.fromCodePoint`. It is used to create a string from a Unicode code point.
 */
export const fromCodePoint: (...codePoints: number[]) => string =
    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition, n/no-unsupported-features/es-builtins
    String.fromCodePoint ??
    ((codePoint: number): string => {
        let output = "";

        if (codePoint > 0xff_ff) {
            codePoint -= 0x1_00_00;
            output += String.fromCharCode(
                ((codePoint >>> 10) & 0x3_ff) | 0xd8_00,
            );
            codePoint = 0xdc_00 | (codePoint & 0x3_ff);
        }

        output += String.fromCharCode(codePoint);
        return output;
    });

/**
 * Replace the given code point with a replacement character if it is a
 * surrogate or is outside the valid range. Otherwise return the code
 * point unchanged.
 */
export function replaceCodePoint(codePoint: number): number {
    if (
        (codePoint >= 0xd8_00 && codePoint <= 0xdf_ff) ||
        codePoint > 0x10_ff_ff
    ) {
        return 0xff_fd;
    }

    return decodeMap.get(codePoint) ?? codePoint;
}

/**
 * Replace the code point if relevant, then convert it to a string.
 *
 * @deprecated Use `fromCodePoint(replaceCodePoint(codePoint))` instead.
 * @param codePoint The code point to decode.
 * @returns The decoded code point.
 */
export function decodeCodePoint(codePoint: number): string {
    return fromCodePoint(replaceCodePoint(codePoint));
}