Fitty, JavaScript text resizing

Makes text fit perfectly to its container. Ideal for flexible and responsive websites.

Use

Download the fitty.min.js file from the /dist folder.

Include the script on your page.

Call fitty like shown below and pass an element reference or a querySelector.

<div id="my-element">Hello World</div>

<script src="fitty.min.js"></script>
<script>
  fitty('#my-element');
</script>

How it works

Fitty calculates the size difference between the parent and child container, then it resizes the child to fit the parent.

Arguments

You can pass the following option properties.

minSize The minimum font size in pixels. Default is 16.

maxSize The maximum font size in pixels. Default is 512. What can I say, I like powers of two.

multiLine Wrap lines when using minimum font size. Default is true.

observeMutations Rescale when element contents is altered. Is set to false when MutationObserver is not supported. Pass true to use the default MutationObserverInit configuration, pass a custom MutationObserverInit config to optimize monitoring based on your project.

Default configuration

{
  subtree: true,
  childList: true,
  characterData: true
}

You can pass custom arguments like this (currently shows default values)

fitty('#my-element', {
  minSize: 16,
  maxSize: 512,
  multiLine: true,
  observeMutations: 'MutationObserver' in window
});

Options

fitty.observeWindow Observe the window for resize and orientationchange events. Default is true.

fitty.observeWindowDelay Redraw delay for when above events are triggered. Default is 100.

Instance API

fit() Force a redraw of the current fitty element.

unsubscribe() Remove the fitty element from the redraw loop and restore it to its original state.

var myFitty = fitty('#my-element');

// force refit
myFitty.fit();

// unsubscribe from fitty
myFitty.unsubscribe();

Fitty API

fitty.fitAll() Refits all fitty instances to their parent containers.

Performance

For optimal performance add a CSS selector to your stylesheet that sets the elements that will be resized to have white-space:nowrap and display:inline-block. If not, Fitty will detect this and will have to restyle the elements itself resulting in a slight performance penalty.

Suppose all elements that you apply fitty to have the class fit, add this CSS selector:

.fit {
  display: inline-block;
  white-space: nowrap;
}

Should you only want to do this when JavaScript is available, add the following to the <head> of your web page.

<script>document.documentElement.classList.add('js');</script>

And change the CSS selector to:

.js .fit {
  display: inline-block;
  white-space: nowrap;
}

Custom Fonts

Fitty does not concern itself with custom fonts. But it will be important to redraw Fitty text after a custom font has loaded (as measurements are probably incorrect at that point).

If you need to use fitty on browsers that don't have CSS Font Loading support (Edge and Internet Explorer)you can use the fantastic FontFaceObserver by Bram Stein to detect when your fonts have loaded.

See an example custom font implementation below.

(function() {

  // no promise support (<=IE11)
  if (!('Promise' in window)) {
    return;
  }

  // called when all fonts loaded
  function redrawFitty() {
    document.documentElement.classList.add('fonts-loaded');
    fitty.fitAll();
  }

  // Native solution, uses CSS Font Loader 
  function native() {

    // load our custom Oswald font
    var fontOswald = new FontFace('Oswald', 'url(assets/oswald.woff2)', {
      style:'normal',
      weight:'400'
    });
    document.fonts.add(fontOswald);
    fontOswald.load();

    // if all fonts loaded redraw fitty
    document.fonts.ready.then(redrawFitty);
  }

  // Fallback, use FontFaceObserver for older browsers
  function fallback() {

    var style = document.createElement('style');
    style.textContent = '@font-face { font-family: Oswald; src: url(assets/oswald.woff2) format("woff2");}'
    document.head.appendChild(style);

    var s = document.createElement('script');
    s.src = 'https://cdnjs.cloudflare.com/ajax/libs/fontfaceobserver/2.0.13/fontfaceobserver.standalone.js';
    s.onload = function() {
      new FontFaceObserver('Oswald').load().then(redrawFitty);    
    };
    document.body.appendChild(s);
  }

  // CSS Font Load Supported?
  if ('fonts' in document) {
    native();
  }
  else {
    fallback();
  }

}());

Notes

Will not work if the element is not part of the DOM.

Tested

Modern browsers
IE 10+

Versioning

Versioning follows Semver. Within 24 hours we moved to version 2.0.

License

MIT

jmsmrgn / fitty