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component-map

Component Map Build Status npm

Not invasive, performant, and garbage collected storage for React components (and more)

ComponentMap allows for most operations WeakMap provides, but it's not a 1:1 shim. In particular, to simplify the implementation it doesn't accept iterable object as a constructor parameter.

ComponentMap it is preconfigured for performant mapping of React classes, but can be easily customized.

ComponentMap promises following:

  • No mutation of provided keys whatsoever (in contrast to most other WeakMap shims)
  • Efficient garbage collection of components if provided with proper WeakMap implementation
  • Decent retrieval performance if no WeakMap is provided

Unfortunately given first promise, it's not possible to prevent memory pollution in case WeakMap is provided. For this reason ComponentMap can be used without WeakMap option only in short-lived sessions, like development or tests.

Usage

Component Map supports subset of WeakMap API.

  • new ComponentMap(options: object) with following options:
    • WeakMap: WeakMap - the WeakMap implementation to use, or undefined, recommended
    • getBucketName: (object) => string - see Configuraton section below, optional
  • #get(key: object): any - returns the value that key corresponds to the key or undefined.
  • #has(key: object): boolean - tells whether there exists a value with given key
  • #set(key: object, value: any) - sets key to given value. The key must be an object.
  • #delete(key: object): boolean - removes the value and returns true if there was a value to delete.

The key option must be an object, by default ComponentMap is optimized to store React components.

Example

class MyComponent { render() { return <div>Hello world</div> } }
 
const components = new ComponentMap({ WeakMap })
components.set(MyComponent, { metadata: 'something' })
// somewhere else 
const meta = components.get(MyComponent).metadata

Configuration

If you wish to use objects other than React components as keys, you can use getBucketName. It allows for specifying custom bucket names. See how ComponentMap is a subclass of BucketMap:

const object = { type: 'MyObject' }
class myMap = new ComponentMap({ getBucketName: (key => key.type) })
myMap.set(MyObject, 'something')

How it works

By default it tries to store components directly into passed WeakMap, if provided. Otherwise it uses custom storage that puts objects into buckets instead of single map, improving retrieval performance a lot. Something like buckets[getBucketName(key)] = value.

ComponentMap doesn't automatically detect WeakMap implementation, but rather allows you to pass it as a constructor parameter. It uses bucketed storage implementation only in case WeakMap is not provided.

License

MIT