fix: resolves #2733

.changeset/pretty-brooms-pull.md

@@ -0,0 +1,5 @@
+---
+"viem": patch
+---
+
+Fixed issue where \`watchBlock\` would not respect the \`emitOnBegin\` property for WebSocket Transports.

src/actions/public/watchBlocks.test.ts

@@ -623,6 +623,8 @@ describe('poll', () => {
       })
       expect(error).toMatchInlineSnapshot('[Error: foo]')
       unwatch()
+
+      vi.restoreAllMocks()
     })
   })
 })
@@ -654,6 +656,27 @@ describe('subscribe', () => {
     expect(typeof blocks[0].number).toBe('bigint')
   })
 
+  describe('emitOnBegin', () => {
+    test('watches for new blocks', async () => {
+      const blocks: OnBlockParameter[] = []
+      const unwatch = watchBlocks(webSocketClient, {
+        emitOnBegin: true,
+        onBlock: (block) => blocks.push(block),
+      })
+      await wait(800)
+      await mine(client, { blocks: 1 })
+      await wait(200)
+      await mine(client, { blocks: 1 })
+      await wait(200)
+      await mine(client, { blocks: 1 })
+      await wait(200)
+      await mine(client, { blocks: 1 })
+      await wait(200)
+      unwatch()
+      expect(blocks.length).toBe(5)
+    })
+  })
+
   describe('behavior', () => {
     test('does not emit when no new incoming blocks', async () => {
       const blocks: OnBlockParameter[] = []

src/actions/public/watchBlocks.ts

@@ -202,9 +202,26 @@ export function watchBlocks<
 
   const subscribeBlocks = () => {
     let active = true
+    let emitFetched = true
     let unsubscribe = () => (active = false)
     ;(async () => {
       try {
+        if (emitOnBegin) {
+          getAction(
+            client,
+            getBlock,
+            'getBlock',
+          )({
+            blockTag,
+            includeTransactions,
+          }).then((block) => {
+            if (!active) return
+            if (!emitFetched) return
+            onBlock(block as any, undefined)
+            emitFetched = false
+          })
+        }
+
         const transport = (() => {
           if (client.transport.type === 'fallback') {
             const transport = client.transport.transports.find(
@@ -225,6 +242,7 @@ export function watchBlocks<
               client.chain?.formatters?.block?.format || formatBlock
             const block = format(data.result)
             onBlock(block, prevBlock as any)
+            emitFetched = false
             prevBlock = block
           },
           onError(error: Error) {