A tag function which makes it possible to create verbose regular expressions in JavaScript. A verbose regular expression is one which ignores the whitespace unless it is escaped with a leading backslash.

vRegExp.js

/**
 * A tag function which can be used to create verbose regular expressions.
 * @license Copyright 2021 - Chris West - MIT Licensed
 * @see https://gist.github.com/westc/dc1b74018d278147e05cac3018acd8e5
 */
function vRegExp(input, ...fillins) {
  let {raw} = input;
  let content = raw[0];
  for (let i = 1, l = raw.length; i < l; i++) {
    content += fillins[i - 1] + raw[i];
  }
  content = content
    // Escapes whitespaces within character classes.
    .replace(
      /(^|[^\\])\[([^\\]+|\\.)\]/g,
      (_, m1, mX) => (m1 + '[' + mX.replace(/\s/g, '\\$&') + ']')
    )
    // Removes whitespaces and JS-style comments.
    .replace(/(\\[^])|\s+|\/\/.*|\/\*[^]*?\*\//g, '$1');
  return new RegExp(
    // Removes the leading flags (eg. "(?i)").
    content.replace(/^(?:\s*\(\?\w+\))+/g, ''),
    // Only keeps the leading flags (eg. "(?i)" becomes "i").
    content.replace(/\(\?(\w+)\)|[^(]+|\(/g, '$1')
  );
}

~example.js

// HIDE \\
console.load('local://vRegExp.js');

// \\
// Regular expression used by srt2vtt to parse subtitles.
var lineBreak = String.raw`(?:\r?\n|\r)`;
var RGX_SRT = vRegExp`
  (?gm)                                   // Global and multiline
  ^\d+$                                   // Subtitle number indicator
  ${lineBreak}                            // Line break
  ^(?<time1a>[\d:]+)[\.,](?<time1b>\d+)   // Line starting with time range
  \s*-->\s*                               // Time range separator
  (?<time2a>[\d:]+)[\.,](?<time2b>\d+)$   // Line ending with time range
  ${lineBreak}                            // Line break
  (?<text>(?:^[^\r\n]+$\r?\n)+)           // One or more lines of text
  ${lineBreak}                            // Line break
`;
console.log(RGX_SRT);

// \\
var srtCode = `
1
00:00:00,000 --> 00:00:01,053
Hello crazy
world!

1
00:00:01,054 --> 00:00:02,987
This is a good test.

`;
console.log(RGX_SRT.exec(srtCode));

~io-app.js

function runIOApp(strRegExp) {
  return vRegExp`${strRegExp}`.toString();
}

~io-config.jsonc

{
  // Where the JS code lies
  "files": ["vRegExp.js", "~io-app.js"],
  // Name of the function responsable for transforming the input into the output.
  "transform": "runIOApp",
  // Input setup
  "input": {
    "language": "text",
    "label": "Input - Verbose Regular Expression",
    "value": "(?i)              // Ignore casing just because we can ;)\n^([a-z0-9_\\.-]+)  // local Part\n@                 // single @ sign\n([0-9a-z\\.-]+)    // Domain name\n\\.                // single Dot\n([a-z]{2,6})$     // Top level Domain"
  },
  // Output setup
  "output": { "language": "javascript", "label": "Output - JavaScript Regular Expression" },
  // Type of YourJS IO-App
  "type": "split",
  // title
  "title": "Verbose Regular Expressions in JavaScript",
  // description
  "description": "Use the custom vRegExp tag function which turns a template string into a regular expression while simulating a verbose regular expression."
}

Run the example file:
https://www.yourjs.com/console/?gist=dc1b74018d278147e05cac3018acd8e5&file=~example.js&skipIntro=1

Here is the corresponding IO App:
https://www.yourjs.com/gist-io/dc1b74018d278147e05cac3018acd8e5