feat: add withResolvers ponyfill (#148)

docs/async/withResolvers.mdx

@@ -0,0 +1,16 @@
+---
+title: withResolvers
+description: Ponyfill for Promise.withResolvers()
+---
+
+### Usage
+
+Creates a new promise and returns the resolve and reject functions along with the promise itself.
+
+The ponyfill for https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/withResolvers
+
+```ts
+const { resolve, reject, promise } = withResolvers()
+
+resolve(42)
+```

src/async/withResolvers.ts

@@ -0,0 +1,30 @@
+interface PromiseWithResolvers<T> {
+  promise: Promise<T>
+  resolve: (value: T | PromiseLike<T>) => void
+  reject: (reason?: any) => void
+}
+
+/**
+ * Creates a new promise and returns the resolve and reject functions along with the promise itself.
+ *
+ * The ponyfill for https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/withResolvers
+ *
+ * @see https://radashi-org.github.io/reference/async/withResolvers
+ * @example
+ * ```ts
+ * const {resolve, reject, promise} = withResolvers()
+ *
+ * resolve(42)
+ * ```
+ */
+export function withResolvers<T>(): PromiseWithResolvers<T> {
+  let resolve: any
+  let reject: any
+
+  const promise = new Promise<T>((res, rej) => {
+    resolve = res
+    reject = rej
+  })
+
+  return { resolve, reject, promise }
+}

src/mod.ts

@@ -39,6 +39,7 @@ export * from './async/reduce.ts'
 export * from './async/retry.ts'
 export * from './async/sleep.ts'
 export * from './async/tryit.ts'
+export * from './async/withResolvers.ts'
 
 export * from './curry/callable.ts'
 export * from './curry/chain.ts'

tests/async/withResolvers.test.ts

@@ -0,0 +1,19 @@
+import * as _ from 'radashi'
+
+describe('withResolvers', () => {
+  test('resolves promise', async () => {
+    const { resolve, promise } = _.withResolvers<number>()
+
+    resolve(42)
+
+    expect(await promise).toBe(42)
+  })
+
+  test('rejects promise', async () => {
+    const { reject, promise } = _.withResolvers<number>()
+
+    reject('Weird error')
+
+    await expect(promise).rejects.toThrowError('Weird error')
+  })
+})