feat: adds size method

Author: rasulomaroff

src/rv.spec.ts

@@ -90,4 +90,37 @@ describe('rv function', () => {
 
         expect(val()).toBe(30)
     })
+
+    describe('size method', () => {
+        it('returns 0 if there is no listeners', () => {
+            const counter = rv(33)
+            expect(counter.size()).toBe(0)
+        })
+
+        it('returns number of listeners', () => {
+            const counter = rv(33)
+            counter.on(() => {})
+            counter.on(() => {})
+            expect(counter.size()).toBe(2)
+        })
+
+        it('correctly recognizes unsubscribes', () => {
+            const counter = rv(33)
+
+            const unsub1 = counter.on(() => {})
+            const unsub2 = counter.on(() => {})
+
+            expect(counter.size()).toBe(2)
+
+            unsub1()
+            expect(counter.size()).toBe(1)
+
+            unsub1()
+            // still one, because we've already unsubscribed from this function
+            expect(counter.size()).toBe(1)
+
+            unsub2()
+            expect(counter.size()).toBe(0)
+        })
+    })
 })

src/rv.ts

@@ -8,7 +8,7 @@ const defaultEq = <T>(oldValue: T, newValue: T): boolean => oldValue === newValu
  * @template T The type of the stored value.
  *
  * @param val The initial value of the reactive variable.
- * @param options Optional configuration for the reactive variable.
+ * @param opts Optional configuration for the reactive variable.
  *
  * @returns A reactive variable function that allows getting, setting, and listening for updates.
  *
@@ -53,22 +53,22 @@ const defaultEq = <T>(oldValue: T, newValue: T): boolean => oldValue === newValu
  * positiveVar(5) // there will be no logs
  * ```
  */
-export function rv<T>(val: T, options?: RvInitOptions<T>): Rv<T> {
-    const { eq = defaultEq, on } = options ?? <RvInitOptions<T>>{}
+export function rv<T>(val: T, opts?: RvInitOptions<T>): Rv<T> {
+    const { eq = defaultEq, on } = opts ?? <RvInitOptions<T>>{}
 
     const listeners = new Set<Listener<T>>()
 
     if (on) listeners.add(on)
 
-    const fn: Rv<T> = (...args: [] | [newValue: T, options?: RvOptions<T>]): T => {
+    const fn: Rv<T> = (...args: [] | [newValue: T, opts?: RvOptions<T>]): T => {
         if (args.length === 0) return val
 
-        const [newValue, options] = args
+        const [newValue, opts] = args
 
         let eqfn: EqualFn<T> = eq
 
-        if (typeof options?.eq !== 'undefined') {
-            eqfn = options.eq === false ? defaultEq : options.eq
+        if (typeof opts?.eq !== 'undefined') {
+            eqfn = opts.eq === false ? defaultEq : opts.eq
         }
 
         if (eqfn(val, newValue)) return val
@@ -81,6 +81,9 @@ export function rv<T>(val: T, options?: RvInitOptions<T>): Rv<T> {
         return val
     }
 
+    fn.off = (f): void => void listeners.delete(f)
+    fn.size = (): number => listeners.size
+
     fn.on = (listener): CleanupFn => {
         listeners.add(listener)
 
@@ -97,6 +100,7 @@ export function rv<T>(val: T, options?: RvInitOptions<T>): Rv<T> {
  * The function is immediately executed to determine the initial value.
  *
  * @template T The type of the stored value.
+ *
  * @param init A function that returns the initial value.
  * @param options Optional configuration for equality comparison and event listeners.
  *

src/types.ts

@@ -66,7 +66,19 @@ export interface Rv<T> {
      *
      * @returns A cleanup function to remove the listener.
      */
-    on(listener: Listener<T>): CleanupFn
+    on: (listener: Listener<T>) => CleanupFn
+    /**
+     * Unsubscribes a listener from value changes.
+     *
+     * @param listener A callback function that is needed to be unsubscribed.
+     */
+    off: (listener: Listener<T>) => void
+    /**
+     * Returns the number of listeners for this reactive variable.
+     *
+     * @returns listener count.
+     */
+    size: () => number
 }
 
 /**
@@ -113,5 +125,5 @@ export interface RvInit {
      *
      * @returns A reactive variable function.
      */
-    fn<T>(init: () => T, options?: RvInitOptions<T>): Rv<T>
+    fn: <T>(init: () => T, options?: RvInitOptions<T>) => Rv<T>
 }