webdash-readme-preview/bower_components/polymer/lib/utils/mixin.html

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<link rel="import" href="boot.html">

<script>

(function() {

  'use strict';

  // unique global id for deduping mixins.
  let dedupeId = 0;

  /**
   * @constructor
   * @extends {Function}
   */
  function MixinFunction(){}
  /** @type {(WeakMap | undefined)} */
  MixinFunction.prototype.__mixinApplications;
  /** @type {(Object | undefined)} */
  MixinFunction.prototype.__mixinSet;

  /* eslint-disable valid-jsdoc */
  /**
   * Wraps an ES6 class expression mixin such that the mixin is only applied
   * if it has not already been applied its base argument. Also memoizes mixin
   * applications.
   *
   * @memberof Polymer
   * @template T
   * @param {T} mixin ES6 class expression mixin to wrap
   * @return {T}
   * @suppress {invalidCasts}
   */
  Polymer.dedupingMixin = function(mixin) {
    let mixinApplications = /** @type {!MixinFunction} */(mixin).__mixinApplications;
    if (!mixinApplications) {
      mixinApplications = new WeakMap();
      /** @type {!MixinFunction} */(mixin).__mixinApplications = mixinApplications;
    }
    // maintain a unique id for each mixin
    let mixinDedupeId = dedupeId++;
    function dedupingMixin(base) {
      let baseSet = /** @type {!MixinFunction} */(base).__mixinSet;
      if (baseSet && baseSet[mixinDedupeId]) {
        return base;
      }
      let map = mixinApplications;
      let extended = map.get(base);
      if (!extended) {
        extended = /** @type {!Function} */(mixin)(base);
        map.set(base, extended);
      }
      // copy inherited mixin set from the extended class, or the base class
      // NOTE: we avoid use of Set here because some browser (IE11)
      // cannot extend a base Set via the constructor.
      let mixinSet = Object.create(/** @type {!MixinFunction} */(extended).__mixinSet || baseSet || null);
      mixinSet[mixinDedupeId] = true;
      /** @type {!MixinFunction} */(extended).__mixinSet = mixinSet;
      return extended;
    }

    return /** @type {T} */ (dedupingMixin);
  };
  /* eslint-enable valid-jsdoc */

})();

</script>