MultiMap implementation for ECMAScript/JavaScript

MultiMap.js

export class MultiMap {
  #entries = new Map()
  #size = 0

  get size() {
    return this.#size
  }

  clear() {
    this.#entries.clear()
    this.#size = 0
  }

  delete(key, value) {
    const entries = this.#entries
    const values = entries.get(key)
    if (values === undefined) {
      return false
    }
    if (arguments.length < 2) {
      this.#size -= values.size
      return entries.delete(key)
    }
    if (!values.delete(value)) {
      return false
    }
    --this.#size
    if (values.size === 0) {
      entries.delete(key)
    }
    return true
  }

  *entries() {
    for (const [key, values] of this.#entries.entries()) {
      yield [key, values.values()]
    }
  }

  forEach(callbackFn, thisArg) {
    for (const [key, values] of this.#entries.values()) {
      for (const value of values.values()) {
        callbackFn.call(thisArg, key, value, this)
      }
    }
  }

  get(key) {
    return (this.#entries.get(key) ?? Array.prototype).values()
  }

  has(key, value) {
    const entries = this.#entries
    if (arguments.length < 2) {
      return entries.has(key)
    }
    const values = entries.get(key)
    return values !== undefined && values.has(value)
  }

  keys() {
    return this.#entries.keys()
  }

  set(key, value) {
    const entries = this.#entries
    const values = entries.get(key)
    if (values === undefined) {
      entries.set(key, new Set([value]))
    } else {
      values.add(value)
    }
    ++this.#size
    return this
  }

  *values() {
    for (const values of this.#entries.values()) {
      yield* values.values()
    }
  }

  [Symbol.iterator]() {
    return this.entries()
  }
}