Javascript regex for formatting time

Question

Our organization's style guide specifies a date-time in this format: Dec. 31 08:45 a.m.. Our site runs Drupal, which is a PHP-based CMS. Its field formatting templates allow for date-formatting strings specified in the encoding which is defined in HPHP's date() function. It only offers a, which gives pm, and A, which gives me PM, but I don't see anything specifying one with periods.

Unfortunately, there is not an easy way to hook in to the platform to define a custom date format, so I figure the simplest way forward is to do a find-and-replace with javascript. What I want to do is replace instances in the format NN:NN am and NN:NN pm with NN:NN a.m., etc.

Regexes have never been my strong suit. I can match date time format well enough( [0-9][0-9]:[0-9][0-9] pm), but I don't know how to perform the proper replacement.

How can I replace am and pm with properly abbreviated version, when they follow a four-digit time format?

What have you tried so far? Please post the code you've written already. — Marc M.
– Marc M., Commented Oct 23, 2018 at 19:45
@MarcM. Hello, what I've tried so far is what I have already posted in the question: [0-9][0-9]:[0-9][0-9] pm. I don't know how to do the replace part. — user151841
– user151841, Commented Oct 23, 2018 at 19:56

BadHorsie · Accepted Answer · 2018-10-23 19:56:55Z

1

str.replace(/(\d{2}:\d{2}\s?a|p)(m)/, '$1.$2');

answered Oct 23, 2018 at 19:56

BadHorsie

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user151841 · Accepted Answer · 2018-10-23 19:55:41Z

1

An alternative is using the optional handler in the function replace to get the match string and replace the am or pm strings with a.m or p.m respectively.

let str = "Dec. 31 08:45 am",
    result = str.replace(/([\d][\d]:[\d][\d] am|pm)/, function(match) {
      return match.replace('am', 'a.m.').replace('pm', 'p.m.');
    });
    
console.log(result);

edited Oct 23, 2018 at 19:55

user151841

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answered Oct 23, 2018 at 19:50

Ele

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1 Comment

user47589 Over a year ago

I think one replacement using str.replace(/([\d][\d]:[\d][\d]) ([ap])m/, "$1 $2.m.") can work by grouping the A and P together. I admit I haven't tested it extensively.

Poul Bak · Accepted Answer · 2018-10-23 19:58:19Z

1

You can use the following regex and replacement pattern to do, what you want:

Regex: ([0-2][0-9]:[0-5][0-9]\s)(a|p)(m)

Replace: '$1$2.$3.'

How to use:

var text = 'Dec. 31 08:45 am';
text = text.replace(/([0-2][0-9]:[0-5][0-9] )(a|p)(m)/, '$1$2.$3.');

answered Oct 23, 2018 at 19:58

Poul Bak

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Comments

4thex · Accepted Answer · 2018-10-23 20:11:17Z

1

'Dec. 31 08:45 AM, Jan. 1 10:15 pm'.replace(/(\d{2}:\d{2}) (a|p)(m)/ig, (match, p1, p2, p3) => {
  return `${p1} ${p2}.${p3}.`.toLowerCase();
});

yields the result

Dec. 31 08:45 a.m., Jan. 1 10:15 p.m.

answered Oct 23, 2018 at 20:11

4thex

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1 Comment

4thex Over a year ago

The i after the regular expression is needed to ignore case if the input could also be uppercase like AM, and PM. The g is for replacing all occurrences. Otherwise only the first will be replaced. The solution uses some modern syntax that may not work in an older browser.

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