feat: add getType helper

export getType to public API

src/__tests__/__snapshots__/get-type.dts.spec.ts.snap

@@ -0,0 +1,5 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`getType getType(viaToString) (type) should match snapshot: getType getType(viaToString) 1`] = `"\\"[Todo] truncate\\""`;
+
+exports[`getType getType(viaType) (type) should match snapshot: getType getType(viaType) 1`] = `"\\"[Todo] truncate\\""`;

src/__tests__/get-type.dts.spec.ts

@@ -0,0 +1,19 @@
+import { getType } from '../get-type'
+
+// @dts-jest:group getType
+
+const type = '[Todo] truncate'
+type Type = typeof type
+
+const viaType = { type: <Type>type }
+const viaToString = {
+  toString(): Type {
+    return type
+  },
+}
+
+// @dts-jest:pass:snap
+getType(viaType)
+
+// @dts-jest:pass:snap
+getType(viaToString)

src/__tests__/get-type.spec.ts

@@ -0,0 +1,28 @@
+import { getType } from '../get-type'
+
+describe('getType', () => {
+  it('should throw error when action creator does not provide either .type nor toString()', () => {
+    const type = '[Todo] truncate'
+    const actionCreator = () => ({ type })
+
+    expect(() => getType(actionCreator)).toThrow()
+  })
+
+  it('should get action type of action creator via .type', () => {
+    const type = '[Todo] truncate'
+    const actionCreator = Object.assign(() => ({ type }), { type })
+
+    expect(getType(actionCreator)).toBe(type)
+  })
+
+  it('should get action type of action creator via toString()', () => {
+    const type = '[Todo] truncate'
+    const actionCreator = Object.assign(() => ({ type }), {
+      toString() {
+        return type
+      },
+    })
+
+    expect(getType(actionCreator)).toBe(type)
+  })
+})

src/get-type.ts

@@ -0,0 +1,29 @@
+/**
+ * Map action creator to it's contained action type
+ * @description it gets an object with at least a type property or overridden toString method and returns it.
+ * @example
+ * const increment = createAction('[Counter] increment')
+ * getType(increment) //=> '[Counter] increment'
+ * @example
+ * getType({ type: 'TEST' }) //=> 'TEST'
+ * @example
+ * getType({
+ *  toString() { return 'TEST' }
+ * }) //=> 'TEST'
+ */
+export function getType<
+  AC extends { type?: string; toString(): string } | { type: string },
+  Type extends string = AC extends { type: infer T }
+    ? T
+    : AC extends { toString(): infer U }
+    ? U
+    : never
+>(actionCreator: AC) {
+  if (!actionCreator.type && !actionCreator.hasOwnProperty('toString')) {
+    throw new Error(
+      `Action creator that has been passed to getType() does not provide any API to expose action type. You can use createAction() to create an action creator without any unsense errors.`
+    )
+  }
+
+  return <Type>(actionCreator.type || actionCreator.toString())
+}

src/index.ts

@@ -1,2 +1,3 @@
 export * from './action'
 export { createAction, ActionCreator } from './create-action'
+export { getType } from './get-type'