Regex not working in JavaScript

Question

I am trying to make sure that the format people input is exactly this :

.match(/\d{1,2}:\d\d\s((AM)|(PM))/)

Meaning that a user could write :

12:30 AM
2:30 PM

But not :

1:2 A
1:30
PM

It needs to be first two digits, followed by a colon, than two more digits, a space, and either AM or PM. But my regex expression isn't that. What am I missing?

Answer 1

What exactly seems to be the problem?

> "1:2 A".match(/\d{1,2}:\d\d\s((AM)|(PM))/);
null

>"12:30 AM".match(/\d{1,2}:\d\d\s((AM)|(PM))/);
["12:30 AM", "AM", "AM", undefined]

However:

1. You need to ground your expression to the start (^) and end ($) of the string otherwise;

   > "foo 12:30 AM foo".match(/\d{1,2}:\d\d\s((AM)|(PM))/);
   ["12:30 AM", "AM", "AM", undefined]
   

2. Look at RegExp.test() instead, which returns a simpler true/false rather than an array.

   > /^\d{1,2}:\d\d\s((AM)|(PM))$/.test("12:30 AM");
   true
   

A simpler expression which does the same thing could be /^\d{1,2}:\d{2} [AP]M$/