Use the toLocaleString() method to change time formatting to 24 hours. The toLocaleString () method returns a string that represents the date and time.

Convert time in to US format.

const dateObject = new Date();

// in 24 hour format
console.log(
  dateObject.toLocaleString('en-US', {
    hour12: false,
  }),
);

Convert AM/PM Time string to 24 Hours Format

let timeString = "01:02 PM";
let [fullMatch, time, modifier] = timeString.match(/(\d?\d:\d\d)\s*(\w{2})/i);

let [hours, minutes] = time.split(':');

if (hours === '12') {
    hours = '00';
}

if (modifier === 'PM') {
    hours = (parseInt(hours, 10) + 12).toString();
}

convertedTime = hours + ":" + minutes;

console.log(convertedTime);