Computed bindings in auto-binding templates in Polymer 1.0

Question

How can I define computed bindings in auto-binding templates (i.e. those declared as <template is='dom-bind'>...</template>)?

Answer 1

Simply assign the computed binding directly to the template element via a script, making sure that the involved properties are initialized after the definition of the computed binding.

Example:

<template is="dom-bind">
  <div>
    <input value="{{text::input}}">
  </div>
  <div>[[describe(text)]]</div>
</template>

<script>
  (function() {
    var template = document.querySelector('template[is="dom-bind"]');

    template.describe = function(text) {
      if (text) {
        return 'You entered "' + text + '", which is ' + text.length + ' characters long.';
      } else {
        return 'You didn\'t even enter a thing! Shame on you.';
      }
    };

    template.text = '';
  })();
</script>