fix: Don't crash on bigints

src/__tests__/request.test.ts

@@ -343,6 +343,21 @@ describe('request', () => {
                 'application/x-www-form-urlencoded'
             )
         })
+
+        it('converts bigint properties to string without throwing', () => {
+            request(
+                createRequest({
+                    url: 'https://any.posthog-instance.com/',
+                    method: 'POST',
+                    compression: Compression.Base64,
+                    data: { foo: BigInt('999999999999999999999') },
+                })
+            )
+            expect(mockedXHR.send.mock.calls[0][0]).toMatchInlineSnapshot(
+                `"data=eyJmb28iOiI5OTk5OTk5OTk5OTk5OTk5OTk5OTkifQ%3D%3D"`
+            )
+            expect(mockedXHR.setRequestHeader).toHaveBeenCalledWith('Content-Type', 'application/x-www-form-urlencoded')
+        })
     })
 
     describe('sendBeacon', () => {

src/request.ts

@@ -41,8 +41,17 @@ export const extendURLParams = (url: string, params: Record<string, any>): strin
     return `${baseUrl}?${newSearch}`
 }
 
+export const jsonStringify = (data: any, space?: string | number): string => {
+    // With plain JSON.stringify, we get an exception when a property is a BigInt. This has caused problems for some users,
+    // see https://github.com/PostHog/posthog-js/issues/1440
+    // To work around this, we convert BigInts to strings before stringifying the data. This is not ideal, as we lose
+    // information that this was originally a number, but given ClickHouse doesn't support BigInts, the customer
+    // would not be able to operate on these numerically anyway.
+    return JSON.stringify(data, (_, value) => (typeof value === 'bigint' ? value.toString() : value), space)
+}
+
 const encodeToDataString = (data: string | Record<string, any>): string => {
-    return 'data=' + encodeURIComponent(typeof data === 'string' ? data : JSON.stringify(data))
+    return 'data=' + encodeURIComponent(typeof data === 'string' ? data : jsonStringify(data))
 }
 
 const encodePostData = ({ data, compression }: RequestOptions): EncodedBody | undefined => {
@@ -51,7 +60,7 @@ const encodePostData = ({ data, compression }: RequestOptions): EncodedBody | un
     }
 
     if (compression === Compression.GZipJS) {
-        const gzipData = gzipSync(strToU8(JSON.stringify(data)), { mtime: 0 })
+        const gzipData = gzipSync(strToU8(jsonStringify(data)), { mtime: 0 })
         const blob = new Blob([gzipData], { type: CONTENT_TYPE_PLAIN })
         return {
             contentType: CONTENT_TYPE_PLAIN,
@@ -61,7 +70,7 @@ const encodePostData = ({ data, compression }: RequestOptions): EncodedBody | un
     }
 
     if (compression === Compression.Base64) {
-        const b64data = _base64Encode(JSON.stringify(data))
+        const b64data = _base64Encode(jsonStringify(data))
         const encodedBody = encodeToDataString(b64data)
 
         return {
@@ -71,7 +80,7 @@ const encodePostData = ({ data, compression }: RequestOptions): EncodedBody | un
         }
     }
 
-    const jsonBody = JSON.stringify(data)
+    const jsonBody = jsonStringify(data)
     return {
         contentType: CONTENT_TYPE_JSON,
         body: jsonBody,