advanced scope

v-memo directive for performance optimization

v-memo is only supported in 3.2+. It memoizes a sub-tree of the template and can be used on both elements and components. The directive expects a fixed-length array of dependency values to compare for memoization. If every value in the array was the same as the last render, then updates for the entire sub-tree will be skipped, and even Virtual DOM VNode creation will be skipped since the memoized copy can be reused. It is important to specify the memoization array correctly to avoid skipping updates that should be applied. v-memo with an empty dependency array would be functionally equivalent to v-once.