What are custom options merging strategies?

Vue uses the default strategy which overwrites the existing value while custom options are merged. But if you want a custom option merged using custom login then you need to attach a function to Vue.config.optionMergeStrategies

For the example, the structure of myOptions custom option would be as below,

Vue.config.optionMergeStrategies.myOption = function (toVal, fromVal) {
// return mergedVal
}

Let's take below Vuex 1.0 merging strategy as an advanced example,

const merge = Vue.config.optionMergeStrategies.computed
Vue.config.optionMergeStrategies.vuex = function (toVal, fromVal) {
if (!toVal) return fromVal
if (!fromVal) return toVal
return {
getters: merge(toVal.getters, fromVal.getters),
state: merge(toVal.state, fromVal.state),
actions: merge(toVal.actions, fromVal.actions)
}
}