5 Ways to Implement Email Validation in JavaScript

Ensuring email addresses are valid is fundamental for clean data and reliable communication. We'll walk through three JavaScript validation techniques, providing functional code for each. We will then analyze the shortcomings of these methods and demonstrate how Abstract API offers a more dependable solution to these common problems.

How to Implement Email Validation in JavaScript

Here are three common techniques to validate email addresses with JavaScript. Each approach has a different implementation, from native browser features to specialized libraries, with functional code for each.

HTML Constraint Validation API

This method leverages the browser’s built-in parser that supports the HTML input element with a "type" attribute set to "email". JavaScript's role is simply to trigger the validity check, which means you do not need to maintain a validation pattern.

The browser’s implementation applies the WHATWG email grammar. It automatically flags issues like "patternMismatch" or "typeMismatch". Developers retain full programmatic control through functions like "reportValidity()" or by the creation of custom messages.

<input id="mail" type="email" required>
<script>
function isValid() {
 const el = document.getElementById('mail');
 return el.checkValidity(); // boolean
}
</script>

A Single Regular Expression

A regular expression offers a pragmatic but aggressive way to validate emails. This pattern approximates the RFC 5322 standard and can cover quoted local parts, domain literals, and most ASCII special characters.

This single expression covers more than 99% of email addresses found in production environments. However, the pattern is intentionally complex and unreadable, so any modification creates a risk of regressions, a topic often discussed by developers.

const rfc5322 = /^(?:[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*|"(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21\x23-\x5b\x5d-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])*")@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|\[(?:25[0-5]|2[0-4]\d|[01]?\d\d?)(?:\.(?:25[0-5]|2[0-4]\d|[01]?\d\d?)){3}\])$/i;

function isValid(email) {
 return rfc5322.test(email);
}

A Library Like Validator.js

You can use an NPM package like "validator" for email validation. This package provides a maintained "isEmail" function that includes options for IP literals, display names, and UTF-8 local parts.

It also allows for the creation of blacklist or whitelist top-level domains. The advantages include shared maintenance, unit tests, and incremental releases that track specification and TLD growth. It works in both browser and Node runtimes.

import validator from 'validator';
validator.isEmail(addr, {
 allow_ip_domain: true,
 allow_utf8_local_part: true,
 host_blacklist: ['example.com']
});

Challenges of Implementing Email Validation in JavaScript

JavaScript-based email validation faces significant hurdles. These range from complex standards and international character sets to the inability to confirm if a mailbox can actually receive mail, which creates unreliable results.

• The RFC 5322 standard is too complex for a single regular expression to cover completely. This leads to unreadable patterns that either reject valid emails or accept invalid ones, a common issue with the regex method.
• Client-side scripts cannot perform DNS or SMTP checks to confirm mailbox existence. All three methods—HTML validation, regex, and libraries like Validator.js—only check syntax, which allows undeliverable addresses to pass as valid.
• Most validation methods, particularly those that rely on a single regular expression, fail to support internationalized addresses. They often reject valid emails that contain Unicode characters or punycode domains, which limits global compatibility.
• Email providers define their own rules for local-parts, such as case sensitivity or support for special characters. A fixed validation rule, used by the HTML API or regex, may incorrectly block real users on certain servers.