What is the best way to parse a time into a Date o

Question

I am working on a form widget for users to enter a time of day into a text input (for a calendar application). Using JavaScript (we are using jQuery FWIW), I want to find the best way to parse the text that the user enters into a JavaScript Date() object so I can easily perform comparisons and other things on it.

I tried the parse() method and it is a little too picky for my needs. I would expect it to be able to successfully parse the following example input times (in addition to other logically similar time formats) as the same Date() object:

• 1:00 pm
• 1:00 p.m.
• 1:00 p
• 1:00pm
• 1:00p.m.
• 1:00p
• 1 pm
• 1 p.m.
• 1 p
• 1pm
• 1p.m.
• 1p
• 13:00
• 13

I am thinking that I might use regular expressions to split up the input and extract the information I want to use to create my Date() object. What is the best way to do this?

Answer 1

Compilation table of other answers

First of all, I can't believe that there is not a built-in functionality or even a robust third-party library that can handle this. Actually, it's web development so I can believe it.

Trying to test all edge cases with all these different algorithms was making my head spin, so I took the liberty of compiling all the answers and tests in this thread into a handy table.

The code (and resulting table) is pointlessly large to include inline, so I've made a JSFiddle:

http://jsfiddle.net/jLv16ydb/4/show

// heres some filler code of the functions I included in the test,
// because StackOverfleaux wont let me have a jsfiddle link without code
Functions = [
    JohnResig,
    Qwertie,
    PatrickMcElhaney,
    Brad,
    NathanVillaescusa,
    DaveJarvis,
    AndrewCetinic,
    StefanHaberl,
    PieterDeZwart,
    JoeLencioni,
    Claviska,
    RobG,
    DateJS,
    MomentJS
];
// I didn't include `date-fns`, because it seems to have even more
// limited parsing than MomentJS or DateJS

Please feel free to fork my fiddle and add more algorithms and test cases

I didn't add any comparisons between the result and the "expected" output, because there are cases where the "expected" output could be debated (eg, should 12 be interpreted as 12:00am or 12:00pm?). You will have to go through the table and see which algorithm makes the most sense for you.

Note: The colors do not necessarily indicate quality or "expectedness" of output, they only indicate the type of output:

• red = js error thrown

• yellow = "falsy" value (undefined, null, NaN, "", "invalid date")

• green = js Date() object

• light green = everything else

Where a Date() object is the output, I convert it to 24 hr HH:mm format for ease of comparison.

Answer 2

Here's an improvement on Joe's version. Feel free to edit it further.

function parseTime(timeString)
{
  if (timeString == '') return null;
  var d = new Date();
  var time = timeString.match(/(\d+)(:(\d\d))?\s*(p?)/i);
  d.setHours( parseInt(time[1],10) + ( ( parseInt(time[1],10) < 12 && time[4] ) ? 12 : 0) );
  d.setMinutes( parseInt(time[3],10) || 0 );
  d.setSeconds(0, 0);
  return d;
}

var tests = [
  '1:00 pm','1:00 p.m.','1:00 p','1:00pm','1:00p.m.','1:00p','1 pm',
  '1 p.m.','1 p','1pm','1p.m.', '1p', '13:00','13', '1a', '12', '12a', '12p', '12am', '12pm', '2400am', '2400pm', '2400', 
  '1000', '100', '123', '2459', '2359', '2359am', '1100', '123p',
  '1234', '1', '9', '99', '999', '9999', '99999', '0000', '0011', '-1', 'mioaw' ];

for ( var i = 0; i < tests.length; i++ ) {
  console.log( tests[i].padStart( 9, ' ' ) + " = " + parseTime(tests[i]) );
}

Changes:

• Added radix parameter to the parseInt() calls (so jslint won't complain).
• Made the regex case-insenstive so "2:23 PM" works like "2:23 pm"

Answer 3

I came across a couple of kinks in implementing John Resig's solution. Here is the modified function that I have been using based on his answer:

function parseTime(timeString)
{
  if (timeString == '') return null;
  var d = new Date();
  var time = timeString.match(/(\d+)(:(\d\d))?\s*(p?)/);
  d.setHours( parseInt(time[1]) + ( ( parseInt(time[1]) < 12 && time[4] ) ? 12 : 0) );
  d.setMinutes( parseInt(time[3]) || 0 );
  d.setSeconds(0, 0);
  return d;
} // parseTime()

var tests = [
  '1:00 pm','1:00 p.m.','1:00 p','1:00pm','1:00p.m.','1:00p','1 pm',
  '1 p.m.','1 p','1pm','1p.m.', '1p', '13:00','13', '1a', '12', '12a', '12p', '12am', '12pm', '2400am', '2400pm', '2400', 
  '1000', '100', '123', '2459', '2359', '2359am', '1100', '123p',
  '1234', '1', '9', '99', '999', '9999', '99999', '0000', '0011', '-1', 'mioaw' ];

for ( var i = 0; i < tests.length; i++ ) {
  console.log( tests[i].padStart( 9, ' ' ) + " = " + parseTime(tests[i]) );
}

Answer 4

If you only want seconds here is a one liner

const toSeconds = s => s.split(':').map(v => parseInt(v)).reverse().reduce((acc,e,i) => acc + e * Math.pow(60,i))

Answer 5

After thoroughly testing and investigating through my other compilation answer, I concluded that @Dave Jarvis's solution was the closest to what I felt were reasonable outputs and edge-case-handling. For reference, I looked at what Google Calendar's time inputs reformatted the time to after exiting the text box.

Even still, I saw that it didn't handle some (albeit weird) edge cases that Google Calendar did. So I reworked it from the ground up and this is what I came up with. I also added it to my compilation answer.

// attempt to parse string as time. return js date object
static parseTime(string) {
    string = String(string);

    var am = null;

    // check if "apm" or "pm" explicitly specified, otherwise null
    if (string.toLowerCase().includes("p")) am = false;
    else if (string.toLowerCase().includes("a")) am = true;

    string = string.replace(/\D/g, ""); // remove non-digit characters
    string = string.substring(0, 4); // take only first 4 digits
    if (string.length === 3) string = "0" + string; // consider eg "030" as "0030"
    string = string.replace(/^00/, "24"); // add 24 hours to preserve eg "0012" as "00:12" instead of "12:00", since will be converted to integer

    var time = parseInt(string); // convert to integer
    // default time if all else fails
    var hours = 12,
        minutes = 0;

    // if able to parse as int
    if (Number.isInteger(time)) {
        // treat eg "4" as "4:00pm" (or "4:00am" if "am" explicitly specified)
        if (time >= 0 && time <= 12) {
            hours = time;
            minutes = 0;
            // if "am" or "pm" not specified, establish from number
            if (am === null) {
                if (hours >= 1 && hours <= 12) am = false;
                else am = true;
            }
        }
        // treat eg "20" as "8:00pm"
        else if (time >= 13 && time <= 99) {
            hours = time % 24;
            minutes = 0;
            // if "am" or "pm" not specified, force "am"
            if (am === null) am = true;
        }
        // treat eg "52:95" as 52 hours 95 minutes 
        else if (time >= 100) {
            hours = Math.floor(time / 100); // take first two digits as hour
            minutes = time % 100; // take last two digits as minute
            // if "am" or "pm" not specified, establish from number
            if (am === null) {
                if (hours >= 1 && hours <= 12) am = false;
                else am = true;
            }
        }

        // add 12 hours if "pm"
        if (am === false && hours !== 12) hours += 12;
        // sub 12 hours if "12:00am" (midnight), making "00:00"
        if (am === true && hours === 12) hours = 0;

        // keep hours within 24 and minutes within 60
        // eg 52 hours 95 minutes becomes 4 hours 35 minutes
        hours = hours % 24;
        minutes = minutes % 60;
    }

    // convert to js date object
    var date = new Date();
    date.setHours(hours);
    date.setMinutes(minutes);
    date.setSeconds(0);
    return date;
}

I feel that this is the closest I can get for my needs, but suggestions are welcome. Note: This is American-centric in that it defaults to am/pm for certain patterns:

• 1 => 13:00 (1:00pm)
• 1100 => 23:00 (11:00pm)
• 456 => 16:56 (4:56pm)

Answer 6

A quick solution which works on the input that you've specified:

function parseTime( t ) {
   var d = new Date();
   var time = t.match( /(\d+)(?::(\d\d))?\s*(p?)/ );
   d.setHours( parseInt( time[1]) + (time[3] ? 12 : 0) );
   d.setMinutes( parseInt( time[2]) || 0 );
   return d;
}

var tests = [
  '1:00 pm','1:00 p.m.','1:00 p','1:00pm','1:00p.m.','1:00p','1 pm',
  '1 p.m.','1 p','1pm','1p.m.', '1p', '13:00','13', '1a', '12', '12a', '12p', '12am', '12pm', '2400am', '2400pm', '2400', 
  '1000', '100', '123', '2459', '2359', '2359am', '1100', '123p',
  '1234', '1', '9', '99', '999', '9999', '99999', '0000', '0011', '-1', 'mioaw' ];

for ( var i = 0; i < tests.length; i++ ) {
  console.log( tests[i].padStart( 9, ' ' ) + " = " + parseTime(tests[i]) );
}

It should work for a few other varieties as well (even if a.m. is used, it'll still work - for example). Obviously this is pretty crude but it's also pretty lightweight (much cheaper to use that than a full library, for example).

Warning: The code doe not work with 12:00 AM, etc.