5 Ways to Validate 10-Digit Phone Numbers in JavaScript

Properly validating 10-digit phone numbers in JavaScript is a fundamental step for maintaining clean user data and preventing form submission errors. We will explore four common ways to handle this, providing working code for each method, before discussing their pitfalls and how Abstract API offers a more robust solution.

How to Implement 10-Digit Phone Number Validation in JavaScript

Here are a few common ways to validate 10-digit phone numbers in JavaScript. Each approach uses different tools, from regular expressions to built-in browser features.

Custom Regular Expression

This method uses a custom regular expression, or regex, to define a pattern for a valid 10-digit North American Numbering Plan (NANP) phone number. The code then tests an input string against this pattern.

The function "isTenDigitUS" returns true if the number is valid and false otherwise. The regex itself has several components that make it effective for this specific task.

• It strips an optional "+1" country code and any whitespace.
• It confirms the area code does not begin with a "0" or "1".
• It permits optional separators like hyphens, spaces, or periods to keep the pattern flexible.
• The test runs in a single pass, which makes it an efficient check.

const NANP10 = /^(?:\+1\s*)?(?:\([2-9]\d{2}\)|[2-9]\d{2})[-.\s]?\d{3}[-.\s]?\d{4}$/;
function isTenDigitUS(v) {
  return NANP10.test(v.trim());
}

Browser Constraint Validation with a Pattern

You can use the browser’s built-in constraint validation API to check phone numbers directly in the HTML. This approach offloads the validation logic to the browser itself.

You add a "pattern" attribute to the HTML "input" tag. The regex pattern, like "\\d{10}", is placed directly in the markup, which means any framework can compose it.

In your JavaScript, you can then call the "checkValidity()" method on the input element to see if the user's entry matches the pattern. You can also read the "ValidityState.patternMismatch" property for the same purpose. More information is available on the MDN web docs.

<!-- In your HTML file -->
<input type="tel" id="phone" pattern="\d{10}" required>

<!-- In your JavaScript file -->
document.getElementById('phone').addEventListener('input', e => {
  if (!e.target.checkValidity()) { /* surface error */ }
});

Challenges of 10-Digit Phone Number Validation

While these methods seem straightforward, they introduce significant reliability and maintenance issues. Relying on patterns alone creates several problems for developers who need accurate data from their users.

• The North American Numbering Plan constantly changes with new overlays and relaxed rules. A custom regular expression or a browser pattern attribute quickly becomes outdated and rejects new, valid phone numbers.
• Users paste numbers in many formats. A single custom regex to handle every permutation with spaces, dashes, and parentheses grows complex and often fails to catch all edge cases from user input.
• Pattern validation only confirms syntax, not existence. A custom regex accepts structurally correct but non-existent numbers, like those in unassigned blocks, which provides a false sense of validity.
• Simple regex patterns in JavaScript only match standard ASCII digits. They fail to validate numbers that use non-ASCII characters, such as full-width or Arabic-Indic digits, which leads to silent validation failures.