I have a variable like this
var time = "12h 55m";
I am only allowed to use H,h,M,m characters in the string. If i have something like this
var time = "12hk 55m";
then it should produce an error. how can I validate this using regex expression.'
looking for something like this
if (stringToTest.match(/^[a-zA-Z0-9]*$/))
Try
/^\d{1,2}[hm]\s+\d{1,2}[hm]$/i It matches 2 digits followed by either h or m, followed by one or more space, followed by 2 digits followed by either h or m
Following will match
"12h 55m".match(/^\d{1,2}[hm]\s+\d{1,2}[hm]$/i) "12m 55h".match(/^\d{1,2}[hm]\s+\d{1,2}[hm]$/i) "2m 55h".match(/^\d{1,2}[hm]\s+\d{1,2}[hm]$/i) "12m 5h".match(/^\d{1,2}[hm]\s+\d{1,2}[hm]$/i) These will not
"122h 555m".match(/^\d{1,2}[hm]\s+\d{1,2}[hm]$/i) 
12h 55h. In the comments above, the OP says they are allowed to use only one h
"12h 55m".match(/^(\d{1,2}h\s+\d{1,2}m)|(\d{1,2}m\s+\d{1,2}h)$/g)The reg in regex stands for regular and your data seems to have a possibility to be irregular. I'd recommend to do the check differently but since you're looking for a regex solution:
/^(\d{2,3}h\s+\d{1,2}m)|(\d{1,2}m\s+\d{2,3}h)$/gi
This will match h and m in either order but will reject if either is in the string twice.
You could use following regex ^\d{1,2}[hmHM]\s\d{1,2}[hmHM]:
^ asserts position at start of the string\d matches a digit (equal to [0-9]){1,2} Quantifier — Matches between 1 and 2 times, as many times as possible, giving back as needed[hmHM] matches a single character in the list hmHM (case sensitive)\s matches any whitespace character\d{1,2}[hmHM] as described above\g modifier: global. All matches (don't return after first match)See following snippet to test it:
var regex = /^\d{1,2}[hmHM]\s\d{1,2}[hmHM]/g; function check(par){ console.log(par.value + " match: " + regex.test(par.value)); }Insert a text in the input <input type="text" id="test" value="" onchange="javascript:check(this)">The accepted answer apparently satisfies the OP. But I noticed that in this comment the OP says that the character symbols should not be repeated. For example, 12h 12h should be invalid but all answers match this. I don't think this can be done using only regex. So here is an alternative solution:
function timeParser(timeStr) { var acChars = ['h', 'H', 'm', 'M']; if ((timeStr.match(/\s/g) || []).length !== 1) return false; var tokens = timeStr.split(' '); for (var token of tokens) { var rx = new RegExp("\\d{1,3}[" + acChars.join("") + "]", "g"); if (!token.match(rx) || token.match(rx).length !== 1 || token !== token.match(rx)[0]) return false; var tc = token.charAt(token.length - 1); acChars.splice(acChars.indexOf(tc), 1); } return true; } var timearr = ["12h 12h", "1m1h 515M", "12hk 55m", "H 12m", "m 12H", "12H 11m", "00m 001h", "20M 1"]; for (var tim of timearr) console.log(timeParser(tim));and 12h 12h is not matched.
12m 55his also valid?65h 097h?"12h 55m".match(/^\d{1,2}[hm]\s+\d{1,2}[hm]$/g)hormallowed