Trying to break up regex into multiple lines in typescript

Question

Because of a linting issue (line too long), I'm trying to break up a regex into two lines. Given the function

function isValidEmail(email) {
    const pattern = new RegExp(`/^(?!.*[._@]{2})[a-z0-9\u00C0-\u00D6\u00D9-\u00F6\u00F9-\u00FC][a-z0-9_.
\u00C0-\u00D6\u00D9-\u00F6\u00F9-\u00FC]*@\w+(\.\w+)?(\.[a-z]{2,3})?\.[a-z]{2,3}$/i`);
    return pattern.test(email.trim());
}

My solution was to use backticks, but it seems that converting a RegExp into a String isn't as straightforward as it seems in Javascript (to be clear, I'm writing typescript and having it transpiled to Javascript.) When I debug the resulting javascript file, the pattern variable becomes

/\/^(?!.*[._@]{2})[a-z0-9À-ÖÙ-öù-ü][a-z0-9_.
À-ÖÙ-öù-ü]*@w+(.w+)?(.[a-z]{2,3})?.[a-z]{2,3}$\/i/

I'm not sure what's happening the the RegExp, but I haven't been able to get my email RegExp to work aftre breaking it into multiple lines. What is happening in the background, and how do I solve for this?

1) When defining a regex in the constructor notation, never include regex delimiters, 2) In a constructor notation, ``\`` must be doubled to define a literal ``\``. — Wiktor Stribiżew, Aug 27 '17 at 17:35
Just a thought: just use constraint validation? don't have to be that complicated... `elm = document.createElement('input'); elm.type = 'email'; elm.value = email; return elm.validity.valid;` or better yet, only trigger the method on `onsubmit` and not on `onclick` then the method will only run when all fields are valid, put `required` attribute on it if you want — Endless, Aug 27 '17 at 17:37
When you start debating stylistic choices for your regular expressions because they're too long, I would reconsider using regex at all. Some real code, maybe even a proper parser, might be a better option. — ssube, Aug 27 '17 at 17:47
@WiktorStribiżew still unable to get this to work. Can you be more clear about your first point perhaps? — Shwheelz, Aug 27 '17 at 18:01
@WiktorStribiżew this mostly worked, but is there any way to maintain case insensitivity this way? If I remove the / at the end, it eventually gets turned into $i/ instead of $/i. I can remove the /i and it will work, but I lose case insensitivity. — Shwheelz, Aug 27 '17 at 18:27
You are using a constructor notation. See [`RegExp` reference](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp): `new RegExp(pattern[, flags])`. E.g. `new RegExp("word", "ig")` - case insensitive and global. — Wiktor Stribiżew, Aug 27 '17 at 18:30

Trying to break up regex into multiple lines in typescript

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