Javascript Regex Negative Look-ahead (Validating EXACTLY {X} Occurrences and Not More) -

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i think it's called negative look-ahead /x(?!y)/, i'm not sure since started doing regex stuff today. i'm trying validate following:

  // matches aa-00 through zz-99   var regex = /([a-za-z]{2}(?!\b))((-){1})([0-9]{2}(?!\b))/;    var result = regex.test("ev-05"); // should pass   console.log("ev-05: " + result + "\n");    result = regex.test("ev-09"); // should pass   console.log("ev-09: " + result + "\n");    result = regex.test("ev-11"); // should pass   console.log("ev-11: " + result + "\n");    result = regex.test("ev-30"); // should pass   console.log("ev-30: " + result + "\n");    result = regex.test("ev03"); // should fail   console.log("ev03: " + result + "\n");    result = regex.test("e-17"); // should fail   console.log("e-17: " + result + "\n");    result = regex.test("ev-5"); // should fail   console.log("ev-5: " + result + "\n");    result = regex.test("evv-36"); // should fail   console.log("evv-36: " + result + "\n");    result = regex.test("ev-019"); // should fail   console.log("ev-019: " + result + "\n");    result = regex.test("ev--05"); // should fail   console.log("ev--05: " + result + "\n");

here's want:

letter#letter#hyphen#digit#digit (honestly have no idea how describe in readable fashion).

i not want allow input of values of 5 parameters. must 2 letters followed hyphen, followed 2 digits (0-9). want validate there not 3+ letters, nor 3+ digits.

i thought {n} occurrence marker each enough, still returns true when there 3+ letters/digits (as intention of {n} marker). tried negative look-ahead return false if word \b found letters, , non-word \b digits. didn't work either.

if remove negative look-aheads , \b & \b , stick the original:

var regex = /[a-za-z]{2}(-){1}[0-9]{2}/;

then half of values valid, ones extra characters/digits considered valid.

long story short: how ensure there exactly x amount of occurrences something, , return false when there extra? maybe i'm messing nla implementation.

you're making things little more complicated should here. can use this:

/^[a-za-z]{2}-[0-9]{2}$/;

^ match beginning of string , $ match end of string.

this regex allow strings containing 2 letters, followed 1 hyphen , followed 2 digits. can rewrite [0-9] \d in javascript.

/([a-za-z]{2}(?!\b))((-){1})([0-9]{2}(?!\b))/;

this doesn't quite work might expect. (?!\b) prevents word boundary occurring after 2 letters, make valid strings fail.

((-){1}) don't need many parenthesis, if want group those, because there's hardly group. use parentheses capture stuff you'll use later on. {1} redundant well. have never seen single concrete use of {1}. {n} useful when n greater 1.

([0-9]{2}(?!\b)) again, parentheses not quite useful, here, used negated word boundary, should work (similar $ anywhere in string).

if want match such format anywhere in string, can use word boundaries follows:

/\b[a-za-z]{2}-[0-9]{2}\b/;

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