Tagged regular expressions

tagged-regex.js

const tre = (strings, ...values) => {
  const flags = values
    .filter(v => v instanceof RegExp)
    .map(re => re.flags)
    .reduce(
      (a, b) =>
        a +
        b
          .split("")
          .filter(char => !a.includes(char))
          .join("")
    )
  return new RegExp(
    String.raw(
      strings,
      ...values.map(v => (v instanceof RegExp ? v.source : v))
    ),
    flags
  )
}

Usage

const a = /(?:\s+)?/
const b = /[A-Z0-9]/i
const c = /[^\s\u0022\u0027\u003e\u0025\u003d\u0000-\u001f\u007f-\u009f]+/u

const re = tre`(${a}|${b})?${c}`

In the example, re will equal /((?:\s+)?|[A-Za-z0-9])?[^\s\u0022\u0027\u003e\u0025\u003d\u0000-\u001f\u007f-\u009f]+/iu

It is also possible to use comments, like:

const re = tre`(${
a // non-capturing optional whitespace group
}|${
b // alphanumeric character class
})?${
c // you don't even want to know!
}`

Or

const re = tre`(${a /* foo */}|${b /* bar */)`