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onresize and element queries for Polymer 3.0





This package contains two Polymer 3.0 elements:

plastic-resize-aware is a container element that fires an event when its size changes.

plastic-element-query is a non visual element that allows you to use CSS media query style expressions as element queries to apply and remove CSS classes on a target element.

Prior Versions

Please see the element resize-aware for a version that works with Polymer 1.0 or 2.0. The prior version does not include element queries.

Why and How

Sometimes you may need to take some action when the rendered size of an element changes. This element provides the something like the window resize event but for an individual element.

There are many reasons an element's size could change - CSS or class changes, content changes, content of other elements affecting the flow, viewport changes, etc.

The plastic-resize-aware element uses a ResizeObserver which is polyfilled if necessary (so no polling).

The plastic-element-query element depends on a plastic-resize-aware element for size detection. As the reference element changes size the element query gets compared to the new size.


npm install --save plastic-resize-aware

How to Use


<plastic-resize-aware on-element-size-changed="handleChange">
    <img src="[[thePic]]">


<plastic-resize-aware id="pra1">
 any content that could have been in a div
this.$.pra1.addEventListener('element-resize', this.someHandlerName);


The idea with this element is that there is a reference element which must be a plastic-resize-aware element, who's size is monitored. There is also a target element which can be the same as the reference element or a different element. The target element is changed by modifying its classList depending on the queryExpression matching or not matching the reference element's size.

<plastic-resize-aware class="refoo-area right-pin">
    <plastic-element-query query-expression="(min-width: 50em) and (min-height: 40px)" 
       assign-classes="bigfiz  bin baz"></plastic-element-query>
    <plastic-element-query query-expression="(max-width: 225px),(max-height: 20px)" 
    <img src="[[thePic]]">


In this example, the reference element and target element were not specified so both default to the parent plastic-resize-aware.

When the width of the plastic-resize-aware element is at least 50em and the height is at least 40px, the classes bigfiz, bin and baz will be added to the plastic-resize-aware element. When that is no longer true, those classes will be removed.

When the width of the plastic-resize-aware element is at most 225px or the height is at most 20px, the class tinytext will be added to the plastic-resize-aware element. When that is no longer true, that class will be removed.

It is not necessary to locate the plastic-element-query inside plastic-resize-aware nor is it required to apply the CSS modification to the plastic-resize-aware element. The ref-element attribute can be used to point to an instance of plastic-resize-aware by id (string). In code you can set refElement to an id string or an element reference to a plastic-resize-aware.

Similarly the target for applying CSS classes does not have to be a parent plastic-resize-aware or even a plastic-resize-aware at all. Use the target-element attribute to specify an id or set in code to an element reference.

<plastic-resize-aware id="intheflow" class="badabing">
<div id="searcher">...</div>
<plastic-element-query query-expression="(min-width: 50em) and (min-height: 40px)" 
    ref-element="intheflow" target-element="searcher"
    assign-classes="bigfiz bin baz"></plastic-element-query>
<plastic-element-query query-expression="(max-width: 225px),(max-height: 20px)" 
    ref-element="intheflow" target-element="searcher"


plastic-element-query fires a element-query-match event when the matching status of its queryExpression changes. The event detail includes:

   queryExpression: // the query expression 
   matches: // boolean - new matching status
   targetElement: // reference to the target element
   classList: // the list of class names
   width: // width of the ref-element
   height: // height of the ref-element


Please submit issues via the github repository.


Contributions via a PR are welcome.




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  • @polymer/polymer#^3.0.0
MIT License


Polymer 3.0+
Browser Independent