how to digest a PEM key

digest.js

/**
 * returns a base64url based digest of a PEM file
 * @param {*} key 
 */
function digestKey(key) {
    let meat = key.match(/^-{5}[A-Z ]+-{5}[\r\n]{1,2}([a-zA-Z0-9/+\r\n]+={0,3})[\r\n]{1,2}-{5}[A-Z ]+-{5}/)[1];
    if (!meat) throw "unrecognized format";
    meat = meat.replace(/[\r\n]{1,2}/g, '');
    var buf = Buffer.from(meat, 'base64');
    let sha = crypto.createHash('sha256');
    sha.update(buf);
    return sha.digest('base64').replace(/[+\/=]/g, s => s == '+' ? '-' : s == '/' ? '_' : '');
}