Polymer 1.x: Applying iron-media-query inside dom-repeat to determine screen width -


click here jsbin.

i want calculate screen width , assign result number between, say, 0 , 3, example. trying use iron-media-query this.

i expect see (logged console) 1 of queries return value of true , other 3 return false. however, return value of undefined.

what doing wrong?

fyi, after solve this, plan add conditional queryresult() method store value of index when querymatches true.

e.g. 
queryresult: function() {   ...   if(this.querymatches) {     this.set('mediawidth', index);   }   ... }
http://jsbin.com/kamusivebi/1/edit?html,console,output 
<!doctype html> <head>   <meta charset="utf-8">   <base href="https://polygit.org/components/">   <script src="webcomponentsjs/webcomponents-lite.min.js"></script>   <link href="polymer/polymer.html" rel="import"> </head> <body>  <dom-module id="x-element">  <template>   <style></style>    <template is="dom-repeat"             id="page"             items="[[queries]]"             >     <iron-media-query id="query"                       full                       query="[[item]]"                       query-matches="{{querymatches}}"                       >       <span hidden>{{queryresult(index)}}</span>     </iron-media-query>   </template>  </template>  <script>   (function(){     polymer({       is: "x-element",       properties: {         querymatches: boolean,         queries: {           type: object,           value: function() {             return [               '(max-width:  699px)'                         ,               '(min-width:  700px) , (max-width:  899px)' ,               '(min-width:  900px) , (max-width: 1124px)' ,               '(min-width: 1125px)'                         ,             ];           },         },       },       queryresult: function(index) {         this.set('mediawidth', index);         console.log('mediawidth', this.mediawidth);         console.log('querymatches', this.querymatches);       },     });   })(); </script>  </dom-module>  <x-element></x-element>  </body>

two problems:

  1. you're incorrectly binding results of each iron-media-query single querymatches property, each iteration overwrite results of previous iteration. correct this, bind sub-property of item iterator (e.g., item.querymatches), requires changing type of queries string array object array. then, pass item.querymatches queryresult().

  2. your demo missing html import <iron-media-query>, querymatches undefined.

here's demo corrections:

<head>    <meta charset="utf-8">    <base href="https://polygit.org/polymer+:1.7.0/components/">    <script src="webcomponentsjs/webcomponents-lite.min.js"></script>    <link href="polymer/polymer.html" rel="import">    <link href="iron-media-query/iron-media-query.html" rel="import">  </head>  <body>    <dom-module id="x-element">      <template>        <template is="dom-repeat"                  id="page"                  items="[[queries]]"                  >          <iron-media-query id="query"                            full                            query="[[item.q]]"                            query-matches="{{item.querymatches}}"                            >          </iron-media-query>          <span hidden>[[queryresult(index, item.querymatches)]]</span>          <div>[[item.q]]: [[item.querymatches]]</div>        </template>      </template>        <script>        htmlimports.whenready(function() {          polymer({            is: 'x-element',            properties: {              queries: {                type: object,                value: function() {                  return [                    { q: '(max-width:  699px)'                         },                    { q: '(min-width:  700px) , (max-width:  899px)' },                    { q: '(min-width:  900px) , (max-width: 1124px)' },                    { q: '(min-width: 1125px)'                         },                  ];                },              },            },            queryresult: function(index, querymatches) {              console.log('index', index, 'querymatches', querymatches);            }          });        });      </script>      </dom-module>      <x-element></x-element>    </body>

codepen


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