polymer/src/utils/render-status.html

<!--
@license
Copyright (c) 2014 The Polymer Project Authors. All rights reserved.
This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
Code distributed by Google as part of the polymer project is also
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-->
<link rel="import" href="boot.html">

<script>
(function() {

  'use strict';

  let scheduled = false;
  let beforeRenderQueue = [];
  let afterRenderQueue = [];

  function schedule() {
    scheduled = true;
    // before next render
    requestAnimationFrame(function() {
      scheduled = false;
      flushQueue(beforeRenderQueue);
      // after the render
      setTimeout(function() {
        flushQueue(afterRenderQueue);
      });
    });
  }

  function flushQueue(queue) {
    for (let i=0; i<queue.length; i++) {
      try {
        queue[i]();
      } catch(e) {
        setTimeout(() => {
          throw e;
        })
      }
    }
    queue.length = 0;
  }

  Polymer.RenderStatus = {

    beforeNextRender: function(cb) {
      if (!scheduled) {
        schedule();
      }
      beforeRenderQueue.push(cb);
    },

    afterNextRender: function(cb) {
      if (!scheduled) {
        schedule();
      }
      afterRenderQueue.push(cb);
    }

  };

})();
</script>