Exploring the WeakMap Feature in JS

In the previous part of this series, we explored the basics of WeakMaps in JavaScript. In this part, we will look at two common use cases for WeakMaps: caching and storing metadata for DOM nodes.

Caching

WeakMaps can be used for caching values that are expensive to compute. The cache can be keyed by the input to the computation, and the value can be the result of the computation.

Here's an example of how a WeakMap can be used to cache the results of a function:

const cache = new WeakMap();

function computeExpensiveValue(obj) {
  if (cache.has(obj)) {
    return cache.get(obj);
  }

  const result = obj.someExpensiveComputation();
  cache.set(obj, result);
  return result;
}

In this example, the cache variable is a WeakMap that is used to store the result of an expensive computation, keyed by the input object obj. The computeExpensiveValue function checks if the cache already contains the result for the input obj, and if so, returns it. If the result is not in the cache, the function computes the result using obj.someExpensiveComputation(), stores the result in the cache, and returns it.

Using a WeakMap for caching has several advantages. First, it avoids the need to recompute the value for the same input object multiple times. Second, the cached values are automatically cleaned up by the garbage collector when the input object is no longer needed, which helps avoid memory leaks.

Storing Metadata for DOM Nodes

WeakMaps can also be used to store metadata for DOM nodes that should not be exposed as properties of the node object itself. This can be useful for storing data that is associated with a node, but is not relevant to the rendering or behavior of the node.

Here's an example of how a WeakMap can be used to store metadata for a DOM node:

const nodeData = new WeakMap();

function setNodeMetadata(node, metadata) {
  nodeData.set(node, metadata);
}

function getNodeMetadata(node) {
  return nodeData.get(node);
}

In this example, nodeData is a WeakMap that is used to store metadata for a DOM node. The setNodeMetadata function takes a node and some metadata as input, and stores the metadata in the nodeData WeakMap using the node as the key. The getNodeMetadata function takes a node as input and returns the metadata associated with that node from the nodeData WeakMap.

Using a WeakMap to store metadata for DOM nodes helps avoid conflicts with other properties or libraries that may be using the same property names. It also ensures that the metadata is automatically cleaned up by the garbage collector when the node is no longer needed.

Exploring the WeakMap Feature in JS - Part 2

Caching

Storing Metadata for DOM Nodes