Variables in regex [duplicate]

Question

I am trying to use variables in a regular expression, in JavaScript.

Consider this function that will extract all the text between <b> and </b> tags in a given string

function Tags_Content_B(html)
{
 return html.match(/<b>(.*?)<\/b>/g).map(function(val){return val.replace(/<\/?b>/g,'');});
}

To make the function more generic, I would like to add a second parameter: the tag I want to extract content from. Following other examples on how to use variables in regex, I tried this

function Tags_Content(html, tag)
{
 var match_exp   = new RegExp("/<" + tag + ">(.*?)<\/" + tag + ">/g");
 var replace_exp = new RegExp("/<\/?" + tag +">/g");

 return html.match(match_exp).map(function(val){return val.replace(replace_exp,'');});
}

However it doesn't work, no matches, no replacements. Any hint on what am I doing wrong?

Please don't use regular expressions to parse HTML... use an industry-standard parser that has actual security measures to prevent XSS attacks. — Patrick Roberts
– Patrick Roberts, Commented Jun 3, 2017 at 5:02
This is just a personal, "hobby" project with zero exposure to external and/or professional use — resle
– resle, Commented Jun 3, 2017 at 5:07
Did you read the documentation about RegExp? Have a look at the examples. — Felix Kling
– Felix Kling, Commented Jun 3, 2017 at 5:10
Did you proof-read your post? Tags such as <b> must be delimited by backticks or else they will disappear. — user663031
– user663031, Commented Jun 3, 2017 at 5:10
As the documentation states clearly, when using the RegExp constructor, do not include beginning and ending / characters, and specify the flags (g) as a second parameter. Nor can the parameter to replace be a regexp itself--what would that mean? — user663031
– user663031, Commented Jun 3, 2017 at 5:13

Patrick Roberts · Accepted Answer · 2017-06-03 05:17:05Z

3

With the understanding that you should never actually do this:

function Tags_Content(html, tag) {
  var match_exp = new RegExp("<" + tag + ">(.*?)</" + tag + ">", "g");
  var replace_exp = new RegExp("</?" + tag + ">", "g");

  return html.match(match_exp).map(function(value) {
    return value.replace(replace_exp, '');
  });
}

console.log(Tags_Content("Let's <b>test</b> the <code>b</code> tag <b>people!</b>", "b"));

edited Jun 3, 2017 at 5:17

answered Jun 3, 2017 at 5:11

Patrick Roberts

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