element-adapter

Renders dom element(s) adaptive according to their own properties, thus allowing "container queries".

It is inspired by EQCSS and Watched Box.

Demo

You can see it in action on this demo

Usage example

Given the following markup

<div class="component A" contenteditable>
  Lorem ipsum dolor sit amet...
</div>

<div class="component B">
  <div>Child One</div>
  <div>Child Two</div>
</div>

<input class="component C" type="text" value="foo" />
<textarea class="component D">bar</textarea>

adaptive behaviours can be added like this

import addAdaptiveBehaviour from 'element-adapter'

function logOrientationChangesToPortrait (element, props) {
  console.debug(element, 'changed:\n', props)
}

addAdaptiveBehaviour({
  target: document.querySelectorAll('.component'),

  queries: {
    [`width >= 6.25em && height < 50%, aspect-ratio <= ${16 / 9}, width >= 680px`]:
      'classA',
      
    'orientation == landscape':
      'classB',
      
    'orientation == portrait':
      logOrientationChangesToPortrait,
      
    'width > 75%':
      'classC',
      
    'characters == 0, characters > 10':
      'classD',
      
    'children >= 2 && children < 5':
      'classE'
  }
})

Here are some queries explained:

1st query:

// [`width >= 6.25em && height < 50%, aspect-ratio <= ${16 / 9}, width >= 680px`]:
//    'classA',

ADD 'classA' WHEN
  (
    width >= 6.25em
    AND
    height < 50% // of the parent container height
  )

  // the coma acts like OR
  OR aspect-ratio <= 16/9

  // the coma acts like OR
  OR width >= 680px

3rd query:

// 'orientation == portrait':
//   (element, props) => {
//     console.debug(element, 'changed:\n', props)
//   },

EXECUTE FUNCTION logOrientationChangesToPortrait WHEN orientation === 'portrait'

6th query:

// 'children >= 2 && children < 5':
//   'classE'

ADD 'classE' WHEN
  children >= 2
  AND
  children < 5

css variables

In addition to css classes, css custom properties ( variables ) are set on watched elements:

property	type	unit
--ea-width	float	px
--ea-height	float	px
--ea-orientation	landscape, portrait or square	-
--ea-aspect-ratio	float	-
--ea-children	integer	-
--ea-characters	integer	-

This allows to write adaptive css even without queries ( see watchedProperties option for additional details ), like in the following example:

input {
  width: calc(var(--ea-characters, 4) * 1ch);
}

Here the targeted input element will grow wider as the number of characters typed increases, with a default set to 4ch.

Note

• editable elements ( input[type=text|email|...], textarea and [contenteditable]) never get the --ea-children property – and internally the children property is set to 0 for queries evaluation

• non-editable elements never get the --ea-characters property – and internally the characters property is set to 0 for queries evaluation

Parameters

Required

target

Can be a single Element, a NodeList or an array of Elements

Optional

queries

Required if no watched property is provided.

queries: {
  'query a': 'cssClassA',
  'query b': 'cssClassB',
  
  'query c': function onQueryMatch (element, props) {
    // Do something when 'query c' matches element props
  },
  ...
}

Note

Function behaviour parameters:

• element is a reference to the DOM element which props the query is run against
• props are the subset of props ({ key: value } pairs) which the query is run against

Formal query syntax

<expression>[,<expression>]*

where <expression> = <comparison>[ && <comparison>]*

  and <comparison> = [ width | height ] <comparator> [ <css percentage> | <css length> ]
                     || aspect-ratio <comparator> <float>
                     || [ children | characters ] <comparator> <integer>
                     || orientation == [ landscape | portrait | square ]
  
  and <comparator> = [ > | >= | < | <= | == ]

watchedProperties

Required if no query is provided.

By default only properties appearing in queries are watched, meaning observers and listeners will be instantated only for these, thus css variables ( --ea-* ) will only be set according to those.

For example, if you have only the following query 'width > 75%' only a ResizeObserver will be instantiate and only dimension related property will be set ( --ea-width, --ea-height, --ea-aspect-ratio and --ea-orientation) ).

If you have only this one 'children >= 2 && children < 5' only a MutationObserver will be instantated and only --ea-children will be set.

So if you don't need queries and only wishes to use css variables, using the watchedProperties option changes the default behaviour: additional properties listed in this array are watched too.

Here is the syntax:

addAdaptiveBehaviour({
  target: document.querySelector('#componentA'),
  watchedProperties: ['characters', 'width']
})

Clean up

The function provided by element-adapter returns a handler object allowing to unregister created listeners and observers when you no longer need adaptive behaviours – before the target is removed from the dom for instance.

It can be used like this:

const { removeAdaptiveBehaviour } = addAdaptiveBehaviour({...})
///
removeAdaptiveBehaviour()

Calling the clean up function will remove any applied behaviours ( css classes and variables ).

Manually applying behaviours

if you use element-adapter with a front-end lib like say VueJs, and you use reactive props to update the class attribute of the element you are adding adaptive behaviours to, like in the following code,

<input ref="email" name="email" :class="{ invalid: usernameFailure }" type="email">

then the classes applied by element-adapter will be stripped every time your component is updated – since the VueJS lib is not aware of the classes imperatively applied outside his scope.

For those cases element-adapter provides a function which, when called, will re-run all the queries and re-apply behavioural classes according to the element new state.

It can be used like this:

mounted () {
  ({ applyAdaptiveBehaviour: this.applyAdaptiveBehaviour } = addAdaptiveBehaviour({
    target: this.$refs.email,

    queries: {
      'chars-between-19-and-28': 'characters >= 19 && characters <= 28',
      'chars-gt-28': 'characters > 28'
    }
  }))
},

updated () {
  // one of the css classes .chars-between-19-and-28 and .chars-gt-28
  // will be added eventually, according to the number of characters
  // typed in the field
  this.applyAdaptiveBehaviour()
}

Note

Function behaviours – as opposed to classes behaviours – don't get re-run when the element state hasn't changed

Browsers compatibility

Tested on Safari, Chrome and Firefox