CODEWITHSUNDEEP
javascriptregexvalidationfloating-point
eightArmCode
eightArmCode

Reputation: 185

Javascript Regex: validating a double/float

Here's the pattern I'm working on:

var re = /(\d{1,2}\.(?=\d{1,2}))/;

What I would like for this to return is a one or two digit number (which will never be greater than 24, since it is for a time mgmt app), which may or may not be followed by a decimal point with either one or two trailing digits, but not more than two.

I'm not sure about the parenthetical substring match mixed with the lookahead. I just guessed and nested them. Ultimately, if my syntax is okay, I think the only thing I am missing is how to suggest that the pattern may or may not have leading digits, and may or may not contain a decimal with trialing digits.

Let me know if you need more info.

Update, Examples:

We are only dealing with time, and no more time than can occur in a single day. 24 would be the highest input.

Valid: 

23.75
1.4 
1
0.5 
0
.2

Invalid:

1.897
%#$#@$#
Words
other characters

Newest Update:

Since this is a decimal, 23.75 works. We are not counting minutes, but rather fractions of hours.

Also, for the record, I tried validating using methods and conditionals, and it was letting letters pass through after the decimals. I have made the decision to go with regex.

Upvotes: 5

Views: 32887

Answers (3)

Floris
Floris

Reputation: 46375

If "any number given will be less than 24", so that doesn't need to be separately tested for, then the following expression will work. 

^\d{0,2}(\.\d{0,2}){0,1}$

See http://rubular.com/r/YDfHr5T5sQ

Tested against:

23.75             pass
1.4               pass
1                 pass
0.5               pass
0                 pass
.2                pass
1.897             fail
%#$#@$#           fail
Words             fail
other characters  fail

Explanation:

^             start matching at the start of the string
\d{0,2}       look for zero to two digits
(   ){0,1}$   look for this next thing zero or one time, then the end of the string
\.\d{0,2}     match exactly one decimal followed by up to two digits

Note - this regex does match the "empty string". You might want to test for that separately if there's a chance that will somehow make its way to this expression...

Simple code to test in your javascript:

var str = "12.345";
var m = str.match(/^\d{0,2}(?:\.\d{0,2}){0,1}$/);
var goodTime;
if (!m) {
    alert(str + " is not a good time");
}
else {
    goodTime = m[0];
    alert("found a good time: " + goodTime);
}

Note - I made a tweak to the regex - adding ?: in the "bit after the decimal" group. This just means "match but don't capture" so the result will return only the match m[0] and not the group .34 in m[1]. It doesn't actually matter since I assign goodTime the value in m[0] (but only if it's a good time). You can see this in action here

Upvotes: 14

da maddin
da maddin

Reputation: 149

What about this one:

([1]?[0-9])|((20)|(21)|(22)|(23)|(24)){0,1}([.][0-9]{0,2})?

Edit: I would advise you to do only simple checks in RegEx and test semantic correctness (eg. less than 24) somewhere else as it gets really complicated. Time would also not allow 23:74 but 23:59...

Upvotes: 0

Anirudha
Anirudha

Reputation: 32797

Well you can try this regex

^(?![3-9]\d|[2][5-9]|24[.])\d{1,2}([.]\d{1,2})?$

But you don't need to use regex here,just parse the string to number and check if it's less than or equal to 24

Upvotes: 0

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