flextype

Scale the font size of an element in proportion to its width... in style. 😎

Full demo here.

Features

• Simple syntax for scaling at different amounts for different widths
• Define your scaling ratios in CSS, allowing you to:
  • easily override within media queries
  • leverage whatever CSS-preprocessor variables you might be using for your site's layout and typography
• No dependencies
• Supports all modern browsers and IE9+^{[see caveat for IE/Edge]}

Install

NPM

npm install flextype --save

Download

• Minified
• Un-minified

CDN

<!-- Minified: -->
<script src="https://unpkg.com/flextype/dist/flextype.min.js"></script>

<!-- Un-minified: -->
<script src="https://unpkg.com/flextype/dist/flextype.js"></script>

Basic usage

1. Add the class js-flextype to the element(s) you want to scale.

   <div class="MyElement js-flextype">Hello</div>

2. In CSS set the percentage of the .js-flextype element's width you want the font size to be on the CSS custom property --flextype. For instance, if you want the font size to be 18px when the element is 500px wide and to scale linearly at that ratio, you would use the percentage 3.6%.

   .MyElement {
     width: 30%;
     float: left;
     /* ... */
     --flextype: 3.6%;
   }

Advanced usage

Alternative syntax

The ratio passed to flextype can also be expressed as a key-value pair written in JSON, where the key is an element width (in pixels) and the value is the desired corresponding font size (in pixels).

.MyElement {
  /* Use valid JSON wrapped in single quotes */
  --flextype: '{ "500": 18 }';
}

Multiple ratios

The font size can be made to scale at different ratios for different width-ranges, flextype will adjust the font size depending on which rules the element's width currently falls between.

.MyElement {
  --flextype: '{ "500": 18, "1000": 22 }';
}

Given those rules we can expect that, for example, when 250px wide .MyElement will have a font size of 9px and when 750px wide .MyElement will have a font size of 20px.

Locking

You can lock the font size in for particular width-ranges by using + and - modifiers on the width keys.

.MyElement {
  --flextype: '{ "250-": 10, "500+": 18, "1000": "22" "1500+": 36 }';
}

The +/- modifiers will prevent the font size from scaling until the next/previous rule becomes active, respectively.

API

Flextype also has a simple javascript interface, which for the most part you shouldn't have to interact with unless you want to do particularly custom stuff.

• Manually force elements to scale outside of the window resize event

  myElement.style.width = '300px';
  flextype.flex();

• Use a custom selector instead of .js-flextype

  const flexer = flextype(document.getElementsByClassName('💪'));
  // Use flexer.flex() to manually scale should you need to
  // Use flexer.destroy() to remove the resize listener and reset the font

• Execute code on an element whenever flextype finishes scaling it

  myElement.addEventListener('flextype:changed', function() {
    // Cycle the hue every 12px change in font size
    const hue = ((parseFloat(this.style.fontSize) % 12) * 360) / 12;
    this.style.color = `hsl(${hue}, 100%, 50%)`;
  });

• Get the suggested font size of an element based on its CSS rules and width

  flextype.getElSize(myElement);

• Set the font size based on CSS rules and width

  flextype.setElSize(myElement);

• Parse a set of rules against a width programmatically

  flextype.size({ '500-': 10, 1500: 20 }, 1000); // = 15

Caveats

1. IE/Edge support

CSS custom properties are supported in the latest versions of all the major browsers except IE and Edge. As a workaround flextype also accepts rules embedded in the ::before pseudo element's content property.

.MyElement::before {
  content: '3.6%';
  display: none;
}

You can use the flextype PostCSS plugin to convert your --flextype declarations into this format for you while Microsoft catches up.

2. Trigger flextype manually after javascript manipulations

The font size of any .js-flextype elements will be scaled immediately when flextype.js is loaded and then again whenever the window is resized. However, if you insert a new .js-flextype element into the DOM after flextype has already initialized, or if you resize a flextype container outside of the normal window resize event, you'll need to manually trigger the resize with:

flextype.flex();

3. Set a width

Flextype bases the font size off the width of the js-flextype element. If the width of the js-flextype element is itself based off the font size of its content (as it is with inline elements, for example) it can't work.