javascript - Variable in RegEx - Turns RegEx Syntax to String - How to avoid? -

in following snippet (example) can see tried build function more comfortable string-replacements in project.

really found out it's necessary connect regex-syntax variable, , found regex-objekt solution in topic.

but after hours of try(outs), realized solution didn't worked, because converts slashes string, , @ end have simple string again.

the following example focused url replace. example, because have slashes in out pattern , input:

function replacethis(valinput, valpattern, valreplace) {      var regex = new regexp('/' + valpattern + '/', "g");    return valinput.replace(regex, valreplace);  }    example_input = 'http://localhost/images/important.jpg';  example_target = '/applications/ampps/www/';  example_pattern = 'http:\/\/localhost\/';    // function  $('#a').html('[result 1] ' + replacethis(example_input, example_pattern, example_target));    // strings (without function)  $('#b').html('[result 2] ' + 'http://localhost/images/important.jpg'.replace(/http:\/\/localhost\//g, '/applications/ampps/www/'));

p {    font-family: verdana;    margin: 2p 5px;  }

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>  <p id="a">a</p>  <p id="b">b</p>

you can see:

var regex = new regexp('/' + valpattern + '/', "g");

which should lookup string like:

'/http://localhost//g'

not liked assumed/wished:

/http://localhost//g

which should lookup string like:

'http://localhost/'

any ideas how handle/solve this? i'm working since hours on that.

when use regexp object notation, pass first argument pattern without / , second argument flags.

and double escape it.

so /\w{0,9}/g new regexp('\\w{0,9}','g');

so function be:

function replacethis(valinput, valpattern, valreplace) {    var regex = new regexp(valpattern , "g");   return valinput.replace(regex, valreplace); }