WeakRef

`WeakRef.prototype.deref`

Returns the target object of the WeakRef if it has not been garbage collected, otherwise returns undefined

Syntax

JavaScript

weakRef.deref()

Return Value

The target object, or undefined if it has been garbage collected

Examples

Basic Usage

const obj = { name: 'Alice' }
const ref = new WeakRef(obj)
const target = ref.deref()
if (target) console.log(target.name) // 'Alice'

Practical Example

class WeakValueMap<K, V extends object> {
  private map = new Map<K, WeakRef<V>>()
  get(key: K): V | undefined {
    const ref = this.map.get(key)
    const value = ref?.deref()
    if (!value) this.map.delete(key)
    return value
  }
  set(key: K, value: V) {
    this.map.set(key, new WeakRef(value))
  }
}

Advanced Usage

const refs: WeakRef<object>[] = []
function trackObject(obj: object) {
  refs.push(new WeakRef(obj))
}
function countAlive(): number {
  return refs.filter(ref => ref.deref() !== undefined).length
}

Understanding WeakRef.prototype.deref

The WeakRef.prototype.deref method in JavaScript returns the target object of the WeakRef if it has not been garbage collected, otherwise returns undefined. It belongs to the WeakRef object and is one of the most widely used methods for working with weakref values in modern JavaScript and TypeScript applications.

The method signature is weakRef.deref(). When called, it returns the target object, or undefined if it has been garbage collected. Understanding when and how to use deref() helps you write more expressive, readable code.

Common use cases for WeakRef.prototype.deref include data transformation, input validation, API response processing, and building reusable utility functions. It works well alongside related methods like weakref-constructor, finalizationregistry-constructor, weakmap-get, enabling you to chain operations together for complex data manipulation pipelines.

Supported in Chrome 84+, Firefox 79+, Safari 14.1+, Edge 84+, Node.js 14.6+.