Best practices for phone entry input in HTML
Tags: html, ux, javascript
Published: 2022-12-12 10:30:56

It's important to accept users' mobile numbers in a variety of formats and to have a lax rule for phone number validation because doing so can make it easier for users to enter their phone numbers accurately and can help prevent errors or problems with the phone number validation process. This can be particularly important in situations where the phone number is being used for important communications, such as receiving security codes or alerts. By allowing users to enter their phone numbers in different formats and by being lenient with the validation process, you can help ensure that the phone number is entered correctly and that the user is able to receive the communications they need.

There are several JavaScript libraries that can be used for accepting and validating phone numbers in a variety of formats. One example is the Google libphonenumber library, which is an open-source library for parsing, formatting, and validating phone numbers. This library can be used to accept phone numbers in a variety of formats and to validate them according to specific rules or requirements. Other similar libraries include jquery.inputmask and Cleave.js.


Here is an example of how you could use the **Google libphonenumber** library to parse, format, and validate a phone number in JavaScript:

```javascript
// Import the libphonenumber library
const libphonenumber = require('libphonenumber-js');

// Get the HTML input element
let phoneInput = document.getElementById('phone-input');

// Listen for the input event on the input element
phoneInput.addEventListener('input', (event) => {
  // Get the value of the input
  let phoneNumber = event.target.value;

  // Parse the phone number using the parse function
  let parsedNumber = libphonenumber.parse(phoneNumber);

  // Format the parsed phone number using the format function
  let formattedNumber = libphonenumber.format(parsedNumber, 'INTERNATIONAL');

  // Set the value of the input to the formatted phone number
  event.target.value = formattedNumber;
});

// Listen for the blur event on the input element
phoneInput.addEventListener('blur', (event) => {
  // Get the value of the input
  let phoneNumber = event.target.value;

  // Parse the phone number using the parse function
  let parsedNumber = libphonenumber.parse(phoneNumber);

  // Validate the parsed phone number using the isValidNumber function
  let isValid = libphonenumber.isValidNumber(parsedNumber);

  // If the phone number is not valid, show an error message
  if (!isValid) {
    alert('Please enter a valid phone number.');
  }
});
```

In this example, the input event listener is used to parse, format, and update the value of the input as the user types. The blur event listener is used to validate the phone number again when the user leaves the input field. Of course, you can customize this example to suit your specific needs and requirements.

Here is an example of how you could use **Cleave.js** to format and validate a phone number in an HTML input:

```javascript
// Import the Cleave library
import Cleave from 'cleave.js';

// Get the HTML input element
let phoneInput = document.getElementById('phone-input');

// Create a new Cleave instance for the input element
let cleave = new Cleave(phoneInput, {
  phone: true,
  phoneRegionCode: 'US'
});

// Listen for the blur event on the input element
phoneInput.addEventListener('blur', (event) => {
  // Get the value of the input
  let phoneNumber = event.target.value;

  // Use the isValid method to validate the phone number
  let isValid = cleave.isValid();

  // If the phone number is not valid, show an error message
  if (!isValid) {
    alert('Please enter a valid phone number.');
  }
});
```

----

## Phone Autocompletion

Autocomplete in HTML forms works by suggesting possible options to the user as they type. When a user starts to enter information into a form field, the browser will typically display a list of options that match the characters that the user has entered so far. The user can then select an option from the list, which will automatically populate the form field with the selected value. This can save time and reduce errors by making it easier for users to select the correct information.


Autocomplete for a user's phone info can work in a similar way to autocomplete in HTML forms. When a user starts to enter their phone number into a form field, the browser may display a list of possible phone numbers that match the characters that have been entered so far. 

It is generally not possible to determine whether a user has used the autocomplete feature of their browser to fill a form input or whether they have entered the information manually. This is because the autocomplete feature is typically handled by the browser itself, and the website or web application does not have direct access to this information.

But you can guess if a user has used the autofill feature by measuring the speed at which they've filled the input field.

To measure the time it takes a user to fill out a HTML form input, you can use JavaScript to capture the time when the user starts filling out the input and the time when they submit the form. You can then calculate the difference between these two times to find out how many milliseconds it took the user to fill out the input.

Here is an example of how you might do this:


```javascript
<form>
  <input id="phone-input" type="text" />
  <button type="submit" onclick="measureTime()">Submit</button>
</form>

<script>
  function measureTime() {
    var startTime = Date.now(); // Capture the current time

    // Wait for the user to fill out the input field and submit the form
    document.getElementById("phone-input").addEventListener("change", function() {
      var endTime = Date.now(); // Capture the time when the form is submitted
      var timeTaken = endTime - startTime; // Calculate the time taken to fill out the input
      alert("It took you " + timeTaken + " milliseconds to fill out the input field.");
    });
  }
</script>
```