optionMergeStrategiesRender.js

Vue.config.optionMergeStrategies.render = (parentVal, childVal) => {
  if (parentVal) {
    const mergedParentVal = function render (...args) {
      args.push([ childVal.apply(this, args) ])
      
      return parentVal.apply(this, args)
    }

    return mergedParentVal
  }

  return childVal
}