Function mergeOptions

packages/runtime-core/src/componentOptions.ts:969–1003

(
  to: any,
  from: any,
  strats: Record<string, OptionMergeFunction>,
  asMixin = false,
)

}

export function mergeOptions(
  to: any,
  from: any,
  strats: Record<string, OptionMergeFunction>,
  asMixin = false,
): any {
  if (__COMPAT__ && isFunction(from)) {
    from = from.options
  }

  const { mixins, extends: extendsOptions } = from

  if (extendsOptions) {
    mergeOptions(to, extendsOptions, strats, true)
  }
  if (mixins) {
    mixins.forEach((m: ComponentOptionsMixin) =>
      mergeOptions(to, m, strats, true),
    )
  }

  for (const key in from) {
    if (asMixin && key === 'expose') {
      __DEV__ &&
        warn(
          `"expose" option is ignored when declared in mixins or extends. ` +
            `It should only be declared in the base component itself.`,
        )
    } else {
      const strat = internalOptionMergeStrats[key] || (strats && strats[key])
      to[key] = strat ? strat(to[key], from[key]) : from[key]
    }
  }
  return to
}

export const internalOptionMergeStrats: Record<string, Function> = {
  data: mergeDataFn,