Javascript check salesforce id validity

isValidSfId.js

function isValidSfId(str) {
    // https://stackoverflow.com/a/29299786/1333724
    if (typeof str !== 'string' || str.length !== 18) {
        return false;
    }

    let upperCaseToBit = (char) => char.match(/[A-Z]/) ? '1' : '0';
    let binaryToSymbol = (digit) => digit <= 25 ? String.fromCharCode(digit + 65) : String.fromCharCode(digit - 26 + 48);

    let parts = [
        str.slice(0,5).split("").reverse().map(upperCaseToBit).join(""),
        str.slice(5,10).split("").reverse().map(upperCaseToBit).join(""),
        str.slice(10,15).split("").reverse().map(upperCaseToBit).join(""),
    ];

    let check = parts.map(str => binaryToSymbol(parseInt(str, 2))).join("");

    return check === str.slice(-3);
}

Organization IDs are mostly 15 characters, and is one of the most important IDs to validate? Is there any way to do that?