nodejs_hexToDouble.js

function hexToDouble1(num){//expensive
    const splittedNum = num.match(/../g);
    const buf = new ArrayBuffer(8);
    const view = new DataView(buf);
    splittedNum.forEach(function (val, index) {
        view.setInt8(index, parseInt(val, 16));
    });
    return view.getFloat64(0, 0);
}

function hexToDouble2(num){ //cheap
    return Buffer.from(num, 'hex').readDoubleBE(0);
}