fix: Add warning and conversion for number distinct_id (#993)

* Add warning and conversion for number distinct_id

* Move test to unit test

functional_tests/identify.test.ts

@@ -3,7 +3,8 @@ import { waitFor } from '@testing-library/dom'
 import { v4 } from 'uuid'
 import { getRequests } from './mock-server'
 import { createPosthogInstance } from './posthog-instance'
-
+import { logger } from '../src/utils/logger'
+jest.mock('../src/utils/logger')
 test('identify sends a identify event', async () => {
     const token = v4()
     const posthog = await createPosthogInstance(token)
@@ -24,6 +25,7 @@ test('identify sends a identify event', async () => {
             })
         )
     )
+    expect(jest.mocked(logger).error).toBeCalledTimes(0)
 })
 
 test('identify sends an engage request if identify called twice with the same distinct id and with $set/$set_once', async () => {

src/__tests__/identify.test.ts

@@ -0,0 +1,39 @@
+import { v4 } from 'uuid'
+import { createPosthogInstance } from '../../functional_tests/posthog-instance'
+import { logger } from '../utils/logger'
+jest.mock('../utils/logger')
+
+describe('identify', () => {
+    // Note that there are other tests for identify in posthog-core.identify.js
+    // These are in the old style of tests, if you are feeling helpful you could
+    // convert them to the new style in this file.
+
+    it('should persist the distinct_id', async () => {
+        // arrange
+        const token = v4()
+        const posthog = await createPosthogInstance(token)
+        const distinctId = '123'
+
+        // act
+        posthog.identify(distinctId)
+
+        // assert
+        expect(posthog.persistence!.properties()['$user_id']).toEqual(distinctId)
+        expect(jest.mocked(logger).error).toBeCalledTimes(0)
+    })
+
+    it('should convert a numeric distinct_id to a string', async () => {
+        // arrange
+        const token = v4()
+        const posthog = await createPosthogInstance(token)
+        const distinctIdNum = 123
+        const distinctIdString = '123'
+
+        // act
+        posthog.identify(distinctIdNum as any)
+
+        // assert
+        expect(posthog.persistence!.properties()['$user_id']).toEqual(distinctIdString)
+        expect(jest.mocked(logger).error).toBeCalledTimes(1)
+    })
+})

src/posthog-core.ts

@@ -52,7 +52,15 @@ import { PostHogSurveys } from './posthog-surveys'
 import { RateLimiter } from './rate-limiter'
 import { uuidv7 } from './uuidv7'
 import { SurveyCallback } from './posthog-surveys-types'
-import { _isArray, _isEmptyObject, _isFunction, _isObject, _isString, _isUndefined } from './utils/type-utils'
+import {
+    _isArray,
+    _isEmptyObject,
+    _isFunction,
+    _isNumber,
+    _isObject,
+    _isString,
+    _isUndefined,
+} from './utils/type-utils'
 import { _info } from './utils/event-utils'
 import { logger } from './utils/logger'
 import { document, userAgent } from './utils/globals'
@@ -1293,6 +1301,11 @@ export class PostHog {
         if (!this.__loaded || !this.persistence) {
             return logger.uninitializedWarning('posthog.identify')
         }
+        if (_isNumber(new_distinct_id)) {
+            logger.error('The first argument to posthog.identify was a number, but it should be a string.')
+            new_distinct_id = (new_distinct_id as number).toString()
+        }
+
         //if the new_distinct_id has not been set ignore the identify event
         if (!new_distinct_id) {
             logger.error('Unique user id has not been set in posthog.identify')