javascript - Using querySelector to find nested elements inside a Polymer template returns null

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javascript - Using querySelector to find nested elements inside a Polymer template returns null

posted Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

javascript - Using querySelector to find nested elements inside a Polymer template returns null

I'm trying to use paper-tabs inside new element (tabs-list) but after print tabs I can't use querySelector to change selected one.

Element code (without style):

<link rel="import" href="../components/polymer/polymer.html">
<link rel="import" href="../sprint-service/sprint-service.html">
<link rel="import" href="../components/paper-tabs/paper-tabs.html">

<polymer-element name="tab-list" attributes="show">
  <template>
    <sprint-service id="service" sprints="{{sprints}}"></sprint-service>   
    <paper-tabs selected="all" valueattr="name" self-end>
      <paper-tab name="all">ALL</paper-tab>
      <template repeat="{{sprint in sprints}}">
        <paper-tab name="{{sprint.id}}">{{sprint.id}}</paper-tab>
      </template>
    </paper-tabs>
  </template>
  <script>
    Polymer('tab-list', {
      ready: function() {
        var tabs = document.querySelector('paper-tabs');
        tabs.addEventListener('core-select', function() {
          list.show = tabs.selected;
        }) 
      } 
    });
  </script>
</polymer-element>

Index.html code (whitout style):

<!doctype html>
<html>

<head>
  <title>unquote</title>
  <meta name="viewport" content="width=device-width, minimum-scale=1.0, initial-scale=1.0, user-scalable=yes">
  <script src="../components/platform-dev/platform.js"></script>
  <link rel="import" href="../components/font-roboto/roboto.html">
  <link rel="import"
    href="../components/core-header-panel/core-header-panel.html">
  <link rel="import"
    href="../components/core-toolbar/core-toolbar.html">
  <link rel="import" href="tab-list.html">
  <link rel="import" href="post-list.html">
</head>

<body unresolved touch-action="auto">
  <core-header-panel>
    <core-toolbar>
      <tab-list></tab-list>
    </core-toolbar>
    <div class="container" layout vertical center>
      <post-list show="all"></post-list>
    </div>
  </core-header-panel>

  <script>

  var list = document.querySelector('post-list');

  </script>
</body>

</html>

But

querySelector('paper-tabs') = *null*

I've tried to put the eventListener in index.html but I have the same problem. can anyone tell me where the problem is?

Thank you very much!

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1 Reply

深蓝 · Answer 1 · 2021-10-23T17:47:33+0000

document.querySelector('paper-tabs');

doesn't find the paper-tabs element, because it is hidden inside the shadow DOM of the tab-list element.

You can simply give paper-tabs an id, say tabs, and access it like so

this.$.tabs

(See http://www.polymer-project.org/docs/polymer/polymer.html#automatic-node-finding.)

There is also the option to access the shadow DOM directly

this.shadowRoot.querySelector('paper-tabs');

If you only want to listen for changes on the paper-tabs selection, you can use a change watcher:

<paper-tabs selected="{{currentTab}}">

Polymer('tab-list', {
  currentTab: 'all',
  currentTabChanged: function() {
    console.log(this.currentTab);
  }
});

(See http://www.polymer-project.org/docs/polymer/polymer.html#change-watchers)

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javascript - Using querySelector to find nested elements inside a Polymer template returns null

javascript - Using querySelector to find nested elements inside a Polymer template returns null

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