How to match specific length of occurrences in RegEx/JavaScript? -

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i have following variable:

var arg = '--test';

the value of arg can start 1 or 2 hypens: - or --, not more.

i want handle , figured should regex problem.

so far, code is:

if(arg.substr(0, 2).match(/-{1,2}/gi)) {     // doing stuff here... }

what slice first 2 characters of string , try test hypen occourence in sliced string, regex not strong side that's i'm stuck.

basically, want test if there's @ least 1 or maximum 2 - hypens in string/argument.

you can restrict number of hyphens (?!-) negative lookahead after ^-{1,2}:

/^-{1,2}(?!-)/

see regex demo

pattern breakdown:

  • ^ - start of string
  • -{1,2} - 1 or 2 hyphens
  • (?!-) - fail match if there hyphen after 2 hyphens @ start.

note check if regex matches given string or not in js, you'd better use regexp#test() method, see demo below.

function tst() {    var arg = document.getelementbyid("test").value;    if (/^-{1,2}(?!-)/.test(arg)) {     // <======== check if string matches pattern      document.getelementbyid("res").innerhtml = arg + " matched";     } else {      document.getelementbyid("res").innerhtml = arg + " failed match";     }  }
<form>   <input id="test" value="---test" placeholder="<input test string>"/>   <input type="submit" onclick="tst()" id="r"/>   <div id="res"/>  </form>


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