Only use the rune for variables that should be reactive — in other words, variables that cause an , or template expression to update. Everything else can be a normal variable. Objects and arrays ( or ) are made deeply reactive, meaning mutation will trigger updates. This has a trade-off: in exchange for fine-grained reactivity, the objects must be proxied, which has performance overhead. In cases where you're dealing with large objects that are only ever reassigned (rather than mutated), use instead. This is often the case with API responses, for example. To compute something from state, use…