Duck typing dropdowns in javascript

example.js

class Select {
  constructor(options, element, selectedOptionsIndex=0, customBehavior={}) {
    this.options = options;
    this.selectedOptionsIndex = selectedOptionsIndex;
    this.el = element;
    // alternative you'd use _.extend
    Object.keys(customBehavior).forEach(key => { this[key] = customBehavior[key] });
  }
  
  render() {
    this.el.append(this.options.map(this.renderOption));
  }
  
  renderOption(option) {
    return `<li>${option}</li>`;
  }
  
}

specialSelect = new Select(someArray, $('.placeholder'), 0, {
  renderOption: function(option) {
  }
});