Converting comman man time to military time

convert.js

function convertPM(time){
    if(time.startsWith('12')){
        return time.replace('PM','');
    }
    return (parseInt(time.split(':'))+12) + time.substring(2, time.length-2);
}

function convertAM(time){
    if(time.startsWith('12')){
        return '00'+time.substring(2, time.length-2);
    }
    return time.substring(0, time.length-2);
}
function main() {
    var time = getTime(); // "HH:MM:SSAM" or "HH:MM:SSPM"
    if(time.indexOf('P')>0)
        console.log(convertPM(time));
    else
        console.log(convertAM(time));
}