Input string test with a regex in JavaScript

Question

I am trying to test a input string of format AWT=10:15;, based on this regex that I wrote: (([AWT]\w\S=)?(\d{0,9}:)?(\d{0,9});).

Problem 1: I am receiving this error: Uncaught TypeError: Cannot read property '0' of undefined when I try to match the string with the regex.

Problem 2: The string seems to come off as valid even after I enter this: AWT=10:15;12 which shouldn't be the case.

Here is my code:

var reg = new RegExp('(([AWT]\w\S=)?(\d{0,9}:)?(\d{0,9});)');
var x = $('td').find('.awt')[0].value; 

console.log(x);        // AWT=10:15;
console.log(String(x).match(reg)); // [";", ";", undefined, undefined, "", index: 9, input: "AWT=10:15;", groups: undefined]

       if(String(x).match(reg)){
            console.log("valid");
        }else{
            console.log("Invalid")
        }

I was wondering if anyone can help me figure out the right regex for the string.

PS: The string needs to be in that exact format: (AWT=[0,9]:[0,9];).

Toto · Accepted Answer · 2020-06-03 12:23:50Z

Your regex (([AWT]\w\S=)?(\d{0,9}:)?(\d{0,9});) means:

(                       # start group 1
    (                       # start group 2
        [AWT]                   # 1 character A or W or T
        \w                      # 1 word character <=> [A-Za-z0-9_]
        \S                      # 1 non space character
        =                       # equal sign
    )?                      # end group 2, optional
    (                       # start group 3
        \d{0,9}                 # from 0 upto 9 digits
        :                       # colon
    )?                      # end group 3, optional
    (                       # start group 4
        \d{0,9}                 # from 0 upto 9 digits
    )                       # end group 4
    ;                       # semicolon
)                       # end group 1

It matches AWT=10:15; as well as:

blahAWT=123456789:123456789;blah
Wx!=123;
12345;

Not sure it's what you want!

According to your requierement “The string needs to be in that exact format: AWT=[0,9]:[0,9];”, this regex will do the job: ^AWT=\d\d:\d\d;$

Explanation:

^           # beginning of string
    AWT=        # literally AWT=
    \d\d        # 2 digits
    :           # a colon
    \d\d        # 2 digits
    ;           # a semicolon
$           # end of string

Use it this way:

var reg = new RegExp('^AWT=\\d\\d:\\d\\d;$');

or, better:

var reg = /^AWT=\d\d:\d\d;$/;

Paul · Accepted Answer · 2020-05-26 23:42:16Z

0

@user120242 is totally right about the cause of your bug.

I just want to add another option instead of escaping the characters. If you use /someRegex/ this is not necessary.

Moreover, if you are always expecting AWT at the beginning, this ([AWT]\w\S=) is not optimal. It means: either A, W or T, then a word character, then a non space character and then =. If it always starts with AWT= use (AWT=).

var reg = /(([AWT]\w\S=)?(\d{0,9}:)?(\d{0,9});)/
var x = $('td').find('.awt')[0].value;

console.log(x); // AWT=10:15;
console.log(String(x).match(reg));

if (String(x).match(reg)) {
  console.log("valid");
} else {
  console.log("Invalid")
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<table>
  <tr>
    <td><input class="awt" value="AWT=10:15;"></td>
  </tr>
</table>

answered May 26, 2020 at 23:42

Paul

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1 Comment

Parth Mehta Over a year ago

thank you for the answer! However, when I tried AWT=10:15;;; or AWT=10:15;73247 it was still giving me those as a valid string.. I would like the regex to be AWT=[0-9]:[0-9];. Anything in the middle besides an int value and anything after the last semi colon should be invalid.

user120242 · Accepted Answer · 2020-06-03 03:17:37Z

0

You need to escape backslashes in the string, or \w becomes w
You need to use ^$ to match on beginning and end, so it only matches if the full string matches

Another option depending on what you are trying to do, is to use negative lookahead (?!.*)
or a capture group behind the last (;.*) where you would check matches for the final match group for content and reject based on that.

console.log('(([AWT]\w\S=)?(\d{0,9}:)?(\d{0,9});)'); // this is not what you want

function matcher(){
var reg = new RegExp('^(([AWT]\\w\\S=)?(\\d{1,9}:)?(\\d{1,9});)$');
var x = $('td').find('input')[0].value;

console.log(x); // AWT=10:15;
console.log(x.match(reg)); // [";", ";", undefined, undefined, "", index: 9, input: "AWT=10:15;", groups: undefined]

if (reg.test(x)) {
  console.log("valid");
} else {
  console.log("Invalid")
}
}

matcher();
$('td').find('input').on('input',matcher);

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<table><tr>
<td><input class="awt" value="AWT=10:15;"></td></tr></table>

edited Jun 3, 2020 at 3:17

answered May 26, 2020 at 23:25

user120242

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2 Comments

Parth Mehta Over a year ago

This works great, however if I test this regex with AWT=; it still accepts it. That is supposed to be considered invalid.

user120242 Over a year ago

Just change {0,9} to {1,9} so it requires at least one character

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