I am trying to replace 4 numbers with a time format. For example if user enters 1234 to be replaced with 12:34

I have found that this regex does this job

let myString = "1234";
myString.replace(/\b(\d{2})(\d{2})/g, '$1:$2')

But now I am trying to figure out how to use this with cases like

34:12 - this should be replaced to 24:12

01:74 - this should be replaced with 01:59

I have found a regex which does that ^([0-1]?[0-9]|2[0-3]):[0-5][0-9], but I am not able to figure out how to combine this with .replace

CodePudding user response：

There is an overload of replace which takes a function which you can use to do any logic you need, such as:

let myString = "1234";

function formatTime(input){
  return input.replace(/\b(\d{2})(\d{2})/, (_,hh,mm) => {
    return `${Math.min(hh,24)}:${Math.min(mm,59)}`
  })
}

console.log(formatTime("1234"));
console.log(formatTime("3412"));
console.log(formatTime("0174"));

CodePudding user response：

You will need to match on the first and second pair of digits and then bound them by their max values. Once you have the bounded values, you can pad the numbers and join them with a colon.

const toTimeString = (value) => {
  const
    [, hours, minutes] = value.match(/^(\d{2})(\d{2})$/),
    hour = `${Math.min( hours, 24)}`.padStart(2, '0'),
    minute = `${Math.min( minutes, 59)}`.padStart(2, '0');
  return `${hour}:${minute}`;
};

console.log(toTimeString('0174')); // 01:59
console.log(toTimeString('3412')); // 24:12

Now, here is a replacer example:

const minPad = (value, min) => `${Math.min(value, min)}`.padStart(2, '0');

const toTimeString = (value) =>
  value.replace(/\b(\d{2})(\d{2})\b/g, (match, hours, minutes) =>
    `${minPad(hours, 24)}:${minPad(minutes, 59)}`);

console.log(toTimeString('0174 3412')); // 01:59 24:12

CodePudding user response：

I do not see any good reason to use regex in your case.
Just a simple function will do the job.

function transformTextToHHMMTimeFormat(text) {
  const hours = Number(text.slice(0, 2))
  const minutes = Number(text.slice(2, 4))
  const hh = Math.min(hours, 24)
  const mm = Math.min(minutes, 59)

  return `${hh}:${mm}`
}