DOM cache API

The DOM cache API can be used to save computations on DOM nodes. Values are cached per node and must not be used before DOM is fully constructed.

Cache key

Each cache must use a unique key. The cache is stored per DOMNode so the key must only be unique per type of computation not per instance.

The cache key is typically Symbol named after the function performing the calculation but any unique string can be used.

const CACHE_KEY = Symbol(myFunction.name);

Type safety (typescript)

Type safety can be archived by augmenting the DOMNodeCache interface:

declare module "html-validate" {
  export interface DOMNodeCache {
    [CACHE_KEY]?: number;
  }
}

This ensures the typescript type system will correctly infer the proper datatypes when storing and fetching values.

Type declaration is optional but strongly recommended. Without type declaration the value is implied to be any and the user must manually ensure it is of the correct type.

Example

const CACHE_KEY = Symbol(myFunction.name);

declare module "html-validate" {
  export interface DOMNodeCache {
    [CACHE_KEY]?: number;
  }
}

export function myFunction(node: HtmlElement): number {
  if (node.cacheExists(CACHE_KEY)) {
    return node.cacheGet(CACHE_KEY);
  }
  const value = expensiveComputation(node);
  return node.cacheSet(CACHE_KEY, value);
}

API

DOMNode.cacheGet<K>(key: K): DOMNodeCache[K] | undefined

Fetch cached value from a DOMNode. Returns undefined if no cached value is present.

DOMNode.cacheSet<K>(key: K, value: DOMNodeCache[K]): DOMNodeCache[K]

Store value on DOMNode.

DOMNode.cacheRemove<K>(key: K): boolean

Remove value from DOMNode. Returns true if a value was present and false if there was none.

DOMNode.cacheExists<K>(key: K): boolean

Check if a value is cached in DOMNode.