function checkComponentDefined (el, name) {
  // Check if element contains the component.
  if (el.components[name] && el.components[name].attrValue) { return true; }

  return isComponentMixedIn(name, el.mixinEls);
}
Check if a component is *defined* for an entity, including defaults and mixins.
Does not check whether the component has been *initialized* for an entity.

@param {string} el - Entity.
@param {string} name - Component name.
@returns {boolean}