Adjust width of input field to its input

Tackling dynamic resizing using CSS and 'ch' unit

By default, CSS presents you with the ch unit. This nifty unit signifies the width of the number 0 in the font of your field. It's perfect to estimate the width an input field needs to accommodate a certain number of characters:

input[type="text"] {
  width: 10ch; /* "Hey, 10 characters can shindig here!" */
}
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But don't uncork that champagne yet! Font metrics aren't set in stone. You'll observe around a 20-30% variance in ch unit width across various typefaces. Think of it as varying ch-ill levels, if you please!

To stay on top of the game:

1. Tweak padding to ensure your actual width is on point.
2. Call upon JavaScript to dynamically adjust the width upon user input. This way, you cover the character count, padding, and font discrepancies.
3. Apply hidden <span> techniques for more precise widths based on actual characters typed. (This one's like hide-and-seek, only cooler).

Navigating through fonts, special characters and user interaction scenarios

From fixed-width typefaces to those special characters that dance to their own tunes, you'll encounter fonts where ch might lead your calculations astray. Here, we need to step up our game and embrace a dynamic approach involving JavaScript and the DOM.

Monitor changes via the input event and let our event listener adjust the width of the input field in real-time. Pair this with the scrollWidth of a hidden <span> that mirrors the input's content and style. The result? An uncannily accurate width calculation!

function resizeInput(input) {
  let hiddenSpan = document.createElement('span');
  hiddenSpan.style.visibility = 'hidden';
  hiddenSpan.style.position = 'absolute';
  hiddenSpan.textContent = input.value || input.placeholder; // "Psst! Ghost text here!"
  
  document.body.appendChild(hiddenSpan);
  let newWidth = Math.max(hiddenSpan.scrollWidth, 10); // "Width so wide it swallows ten pixels whole!" 
  input.style.width = `${newWidth}px`;
  
  document.body.removeChild(hiddenSpan); // "Bye bye, span!"
}

document.querySelector('input[type=text]').addEventListener('input', function() {
  resizeInput(this);
});
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Do note that our good friend resizeInput is tasked with updating input width. We're mindful of placeholders and string-less scenarios, allotting a minimum width if deemed necessary.

Dynamic field size handling and cross-browser compatibility

When we get down to brass tacks with dynamically resizing inputs, it's vital to ensure cross-device and cross-browser compatibility. While modern browsers are more than adept at handling these fields, always test your solution across various environments.

Special considerations for special scenarios

• Cater to Right-to-left (RTL) typing or Input Method Editors (IME) to ensure that your solution is world-ready.
• Placeholders can potentially be wider than the same text typed out by the user. Make sure your solution resizes the input field when only placeholder text is visible.

An optimal responsive setup

Creating a responsive design setup is akin to staging a good play. Here, the wrapping container and the input field are the star-crossed leads. Size the input field absolutely within its container, letting it take cues from the hidden <span>'s measurement technique.

Jennifying your fields (aka using jQuery)

If you're already a fan of jQuery for its event handling and DOM manipulation wonders, here's a jQuery twist to our dynamic resizing input field:

$('input[type="text"]').on('input', function() {
  resizeInput($(this)); // "Size me up, Scotty!"
});
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Emphasizing demos and usability

Good demos and open source projects help your peers get a better hang of the solution and how it can fit their use cases. Always keep a sharp focus on usability and accessibility while designing inputs — make it a solution for the many, not the few!