@open-wc/dedupe-mixin/src/dedupeMixin.js

Dedupe JavaScript Class Mixins

const appliedClassMixins = new WeakMap();

/** Vefify if the Mixin was previously applyed
 * @private
 * @param {function} mixin      Mixin being applyed
 * @param {object} superClass   Class receiving the new mixin
 * @returns {boolean}
 */
function wasMixinPreviouslyApplied(mixin, superClass) {
  let klass = superClass;
  while (klass) {
    if (appliedClassMixins.get(klass) === mixin) {
      return true;
    }
    klass = Object.getPrototypeOf(klass);
  }
  return false;
}

/** Apply each mixin in the chain to make sure they are not applied more than once to the final class.
 * @export
 * @param {function} mixin      Mixin to be applyed
 * @returns {object}            Mixed class with mixin applied
 */
export function dedupeMixin(mixin) {
  return superClass => {
    if (wasMixinPreviouslyApplied(mixin, superClass)) {
      return superClass;
    }
    const mixedClass = mixin(superClass);
    appliedClassMixins.set(mixedClass, mixin);
    return mixedClass;
  };
}