javascript - Format and replace a string with a regular expression -

i have number that's @ least 7 digits long. typical examples: 0000123, 00001234, 000012345

i want transform them become respectively: 01:23, 12:34, 23:45

which mean replacing whole string last 4 characters , putting colon in middle.

i can last 4 digits (\d{4})$ , can 2 groups this: (\d{2})(\d{2})$

with last option, on string 0000123 $1:$2 match gives me 00001:23 want 01:23

i replace string so:

newval = val.replace(/regex/, '$1:$2');

you need match beginning digits \d* (or .* if there can anything):

var val = "0001235";  var newval = val.replace(/^\d*(\d{2})(\d{2})$/, '$1:$2');  console.log(newval);

pattern details:

Insert