Cumbersome time parsing in JavaScript

Question

I need a function to convert time in text from a format with day-part letters to digits. E.g. 4:15PM -> 16:15, 4:15AM -> 4:15AM. Currently I have the following solution

function formatTime(text){
	var find = '([0-9]|0[0-9]|1[0-9]|2[0-3]):[0-5][0-9] (AM|PM)';
	
	var reg = new RegExp(find, 'g');
	
	pos = 0;

	var result;
	var formatedText = "";
	while((result = reg.exec(text)) !== null) {
		if(result[2] == "PM"){
			var hours= parseInt(result[0], 10);
			hours = hours + 12;
			var hoursStr = hours.toString();
			var newTime = hoursStr + result[0].substring(result[1].length,result[0].length - 3);
			
			formatedText += newTime;
			pos = reg.lastIndex;
		} else {
			formatedText += text.replace("AM","").substring(pos, reg.lastIndex);
			pos = reg.lastIndex;
		}
	}
	
	if(pos < text.length){
		formatedText += text.substring(pos, text.length);
	}
	
	return formatedText;
}

console.log(formatTime("Some Text (11:00AM - 1:00PM)"));

I makes nicely cases like console.log(formatTime("Some Text (11:00AM - 1:00PM)"));

But I strugle to make it process console.log(formatTime("Some Text (11:00 AM - 1:00 PM)"));

E.g. 4:15PM -> 16:15, 4:15AM -> 4:15AM So if it's it PM you want to convert the hour, but if it's AM you want to leave the "AM"" in the result? — user663031
– user663031, Commented Dec 21, 2016 at 10:31
How come you didn't try to use a library such as moment.js? Why reinvent the wheel and waste your valuable time? Libraries exist for a reason, don't hesitate to use them. Arguments such as "it's too big for my needs" or "mine works faster" aren't real arguments. People create free software, we should use it - especially if it saves us our time and lets us focus on our work. — Mjh
– Mjh, Commented Dec 21, 2016 at 11:37

Alex T · Accepted Answer · 2016-12-21 10:42:10Z

1

This works for your examples. I've added \\s? to the regex and made a minor change in the logic of cutting time (-2 instead of -3). Also I've moved variables definition to the beginning of the function to reflect hoisting in JavaScript.

function formatTime(text){
    var find = '([0-9]|0[0-9]|1[0-9]|2[0-3]):[0-5][0-9]\\s?(AM|PM)';            
    var reg = new RegExp(find, 'g');            
    var pos = 0;
    var formatedText = "";
    var result, hours, hoursStr, newTime;           

    while ((result = reg.exec(text)) !== null) {
        if (result[2] === "PM") {
            hours= parseInt(result[0], 10);
            hours = hours + 12;
            hoursStr = hours.toString();
            newTime = hoursStr + result[0].substring(result[1].length, result[0].length - 2);

            formatedText += newTime;                    
        } else {
            formatedText += text.replace("AM","").substring(pos, reg.lastIndex);

        }

        pos = reg.lastIndex;
    }

    if (pos < text.length) {
        formatedText += text.substring(pos, text.length);
    }

    return formatedText;
}

edited Dec 21, 2016 at 10:42

answered Dec 21, 2016 at 10:25

Alex T

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1 Comment

user663031 Over a year ago

Works why, because you did what? Why did you not clean up his regexp for him, or fix it to use a regexp literal as he should? What is the purpose of the g flag, and why is there a loop around reg.exec?

mike510a · Accepted Answer · 2016-12-22 11:00:09Z

0

Here's an easier way to do this: Just use two functions. One to convert the hours, and another to match against PM times along with the replace() function.

Easy does it...

function convertTime12to24(time12h) {
  const [time, modifier] = time12h.split(' ');

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

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

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

  return hours + ':' + minutes;
}


function formatTime(i_string) {
  console.log(i_string.replace(/([0-9]|0[0-9]|1[0-9]|2[0-3]):([0-5][0-9])(PM)/gi, function newDate(x) {

    return convertTime12to24(x.replace("PM", " PM"))
  }));
}
formatTime("The time is now 4:15PM");
formatTime("The time is now 12:15PM");
formatTime("The time is now 4:00AM");
formatTime("The time is now 12:00AM");
formatTime("The time is now 11:00PM");

edited Dec 22, 2016 at 11:00

answered Dec 21, 2016 at 10:28

mike510a

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5 Comments

user663031 Over a year ago

But according to OP, he wants to retain the "AM". Also, your code seems to be removing the space following the dash.

mike510a Over a year ago

I simply wanted to point in the right direction - this site really isn't for creating production quality answers for people -- its for helping solve their programming issues -- since I dont know/care how their algorithm works or how it manages to derive the output, I simply noted the typo and then made a correction where it appeared there was a hard coded value which depended on the typo. I would probably do it a different way using the : as a separator then just adding 12 if its PM to the hour part but whatever

mike510a Over a year ago

@torazaburo also it does not say that they want to retain the AM/PM in the OP -- it says 4:15PM -> 16:15

user663031 Over a year ago

The original post clearly says 4:15AM -> 4:15AM, preserving the "AM", and the OP confirmed that in a comment.

mike510a Over a year ago

im re-writing the code to make it way easier -- this is a terrible answer anywas

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