Bug: useEffectEvent retain the first render value when is used inside a component wrapped in memo() #35187

Description

@gffuma

useEffectEvent retains the first render value when it's used inside a component wrapped in memo()

React version: 19.2.0

Steps To Reproduce

Minimal repro:

import{useState,useEffectEvent,useEffect,memo}from"react";functionApp(){const[counter,setCounter]=useState(0);consthello=useEffectEvent(()=>{console.log(counter);});useEffect(()=>{constid=setInterval(()=>{hello();},1000);return()=>clearInterval(id);},[]);return(<div><buttononClick={()=>setCounter(counter+1)}>{counter}</button></div>);}exportdefaultmemo(App);

Link to code example:
https://codesandbox.io/p/sandbox/gj356q

The current behavior

If you click the button and increment the counter you always see 0 in the log. By removing the memo you will see the current counter value.

The expected behavior

See the latest counter value even if the component is wrapped in memo, since the documentation https://react.dev/reference/react/useEffectEvent does not describe any different behavior if component is wrapped in memo.

Metadata

Metadata

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No one assigned

    Labels

    Status: UnconfirmedA potential issue that we haven't yet confirmed as a bug

    Type

    No type

    Projects

    No projects

      Milestone

      No milestone

      Relationships

      None yet

      Development

      No branches or pull requests

      Issue actions

      , 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Add copy buttons to all
       blocks\n(function() {\n function addCopyButtons() {\n document.querySelectorAll('pre code').forEach(function(codeBlock) {\n if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;\n codeBlock.parentElement.setAttribute('data-copy-added', 'true');\n \n var btn = document.createElement('button');\n btn.textContent = 'Copy';\n btn.style.cssText = 'position:absolute;top:4px;right:4px;padding:2px 8px;font-size:11px;background:#4ecdc4;border:none;border-radius:4px;color:#1a1a2e;cursor:pointer;opacity:0.7;transition:opacity 0.2s;';\n btn.onmouseover = function() { this.style.opacity = '1'; };\n btn.onmouseout = function() { this.style.opacity = '0.7'; };\n btn.onclick = function() {\n navigator.clipboard.writeText(codeBlock.textContent).then(function() {\n btn.textContent = 'Copied!';\n setTimeout(function() { btn.textContent = 'Copy'; }, 1500);\n });\n };\n codeBlock.parentElement.style.position = 'relative';\n codeBlock.parentElement.appendChild(btn);\n });\n }\n \n addCopyButtons();\n \n // Re-run on dynamic content\n var observer = new MutationObserver(addCopyButtons);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Add Copy Buttons to Code Blocks");
      }
      } catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
      })();
      (function(){
      try {
      var __m = "github.com";
      var __re = new RegExp('^' + "github\\.com" + '
      
      Skip to content

      Bug: useEffectEvent retain the first render value when is used inside a component wrapped in memo() #35187

      Description

      @gffuma

      useEffectEvent retains the first render value when it's used inside a component wrapped in memo()

      React version: 19.2.0

      Steps To Reproduce

      Minimal repro:

      import{useState,useEffectEvent,useEffect,memo}from"react";functionApp(){const[counter,setCounter]=useState(0);consthello=useEffectEvent(()=>{console.log(counter);});useEffect(()=>{constid=setInterval(()=>{hello();},1000);return()=>clearInterval(id);},[]);return(<div><buttononClick={()=>setCounter(counter+1)}>{counter}</button></div>);}exportdefaultmemo(App);

      Link to code example:
      https://codesandbox.io/p/sandbox/gj356q

      The current behavior

      If you click the button and increment the counter you always see 0 in the log. By removing the memo you will see the current counter value.

      The expected behavior

      See the latest counter value even if the component is wrapped in memo, since the documentation https://react.dev/reference/react/useEffectEvent does not describe any different behavior if component is wrapped in memo.

      Metadata

      Metadata

      Assignees

      No one assigned

        Labels

        Status: UnconfirmedA potential issue that we haven't yet confirmed as a bug

        Type

        No type

        Projects

        No projects

          Milestone

          No milestone

          Relationships

          None yet

          Development

          No branches or pull requests

          Issue actions

          , 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Force GitHub README to respect dark mode\n(function() {\n var style = document.createElement('style');\n style.textContent = '\n .markdown-body {\n color-scheme: dark light;\n }\n .markdown-body pre { background: #161b22 !important; }\n .markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }\n .markdown-body table th, .markdown-body table td { border-color: #30363d !important; }\n .markdown-body img { background: #0d1117; }\n .markdown-body blockquote { border-left-color: #8b949e; }\n .markdown-body hr { border-color: #30363d; }\n ';\n document.head.appendChild(style);\n})();", "GitHub Dark Mode README Fix"); } } catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); } })(); (function(){ try { var __m = "*"; var __re = new RegExp('^' + ".*" + '
          Skip to content

          Bug: useEffectEvent retain the first render value when is used inside a component wrapped in memo() #35187

          Description

          @gffuma

          useEffectEvent retains the first render value when it's used inside a component wrapped in memo()

          React version: 19.2.0

          Steps To Reproduce

          Minimal repro:

          import{useState,useEffectEvent,useEffect,memo}from"react";functionApp(){const[counter,setCounter]=useState(0);consthello=useEffectEvent(()=>{console.log(counter);});useEffect(()=>{constid=setInterval(()=>{hello();},1000);return()=>clearInterval(id);},[]);return(<div><buttononClick={()=>setCounter(counter+1)}>{counter}</button></div>);}exportdefaultmemo(App);

          Link to code example:
          https://codesandbox.io/p/sandbox/gj356q

          The current behavior

          If you click the button and increment the counter you always see 0 in the log. By removing the memo you will see the current counter value.

          The expected behavior

          See the latest counter value even if the component is wrapped in memo, since the documentation https://react.dev/reference/react/useEffectEvent does not describe any different behavior if component is wrapped in memo.

          Metadata

          Metadata

          Assignees

          No one assigned

            Labels

            Status: UnconfirmedA potential issue that we haven't yet confirmed as a bug

            Type

            No type

            Projects

            No projects

              Milestone

              No milestone

              Relationships

              None yet

              Development

              No branches or pull requests

              Issue actions

              , 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Highlight search terms from Google/DuckDuckGo/Bing referrer\n(function() {\n var ref = document.referrer;\n var terms = [];\n \n if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {\n var url = new URL(ref);\n var q = url.searchParams.get('q') || url.searchParams.get('p');\n if (q) {\n terms = q.split(/\\s+/).filter(function(t) { return t.length > 2; });\n }\n }\n \n if (terms.length === 0) return;\n \n var style = document.createElement('style');\n style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';\n document.head.appendChild(style);\n \n function highlight(node) {\n if (node.nodeType === 3) { // text node\n var text = node.textContent;\n var found = false;\n terms.forEach(function(term) {\n var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\\]\\\\]/g, '\\\\') + ')', 'gi');\n if (regex.test(text)) {\n found = true;\n var frag = document.createDocumentFragment();\n var parts = text.split(regex);\n parts.forEach(function(part, i) {\n if (i % 2 === 0) {\n frag.appendChild(document.createTextNode(part));\n } else {\n var span = document.createElement('span');\n span.className = 'userscript-highlight';\n span.textContent = part;\n frag.appendChild(span);\n }\n });\n node.parentNode.replaceChild(frag, node);\n }\n });\n } else if (node.nodeType === 1 && node.childNodes) { // element\n var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];\n if (!skipTags.includes(node.tagName)) {\n Array.from(node.childNodes).forEach(highlight);\n }\n }\n }\n \n highlight(document.body);\n \n // Re-highlight on dynamic content\n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1 || node.nodeType === 3) highlight(node);\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Highlight Search Terms"); } } catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); } })(); (function(){ try { var __m = "*"; var __re = new RegExp('^' + ".*" + '
              Skip to content

              Bug: useEffectEvent retain the first render value when is used inside a component wrapped in memo() #35187

              Description

              @gffuma

              useEffectEvent retains the first render value when it's used inside a component wrapped in memo()

              React version: 19.2.0

              Steps To Reproduce

              Minimal repro:

              import{useState,useEffectEvent,useEffect,memo}from"react";functionApp(){const[counter,setCounter]=useState(0);consthello=useEffectEvent(()=>{console.log(counter);});useEffect(()=>{constid=setInterval(()=>{hello();},1000);return()=>clearInterval(id);},[]);return(<div><buttononClick={()=>setCounter(counter+1)}>{counter}</button></div>);}exportdefaultmemo(App);

              Link to code example:
              https://codesandbox.io/p/sandbox/gj356q

              The current behavior

              If you click the button and increment the counter you always see 0 in the log. By removing the memo you will see the current counter value.

              The expected behavior

              See the latest counter value even if the component is wrapped in memo, since the documentation https://react.dev/reference/react/useEffectEvent does not describe any different behavior if component is wrapped in memo.

              Metadata

              Metadata

              Assignees

              No one assigned

                Labels

                Status: UnconfirmedA potential issue that we haven't yet confirmed as a bug

                Type

                No type

                Projects

                No projects

                  Milestone

                  No milestone

                  Relationships

                  None yet

                  Development

                  No branches or pull requests

                  Issue actions

                  , 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Strip utm_, fbclid, gclid, etc. from all links on page\n(function() {\n var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',\n 'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',\n 'ref', 'ref_src', 'source', 'medium', 'campaign'];\n \n function cleanUrl(url) {\n try {\n var u = new URL(url, window.location.origin);\n var changed = false;\n trackingParams.forEach(function(p) {\n if (u.searchParams.has(p)) {\n u.searchParams.delete(p);\n changed = true;\n }\n });\n return changed ? u.toString() : url;\n } catch (e) {\n return url;\n }\n }\n \n function cleanLinks() {\n document.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n \n cleanLinks();\n \n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1) {\n if (node.tagName === 'A') cleanLinks();\n node.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Remove Tracking Parameters from Links"); } } catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); } })(); (function(){ try { var __m = "youtube.com"; var __re = new RegExp('^' + "youtube\\.com" + '
                  Skip to content

                  Bug: useEffectEvent retain the first render value when is used inside a component wrapped in memo() #35187

                  Description

                  @gffuma

                  useEffectEvent retains the first render value when it's used inside a component wrapped in memo()

                  React version: 19.2.0

                  Steps To Reproduce

                  Minimal repro:

                  import{useState,useEffectEvent,useEffect,memo}from"react";functionApp(){const[counter,setCounter]=useState(0);consthello=useEffectEvent(()=>{console.log(counter);});useEffect(()=>{constid=setInterval(()=>{hello();},1000);return()=>clearInterval(id);},[]);return(<div><buttononClick={()=>setCounter(counter+1)}>{counter}</button></div>);}exportdefaultmemo(App);

                  Link to code example:
                  https://codesandbox.io/p/sandbox/gj356q

                  The current behavior

                  If you click the button and increment the counter you always see 0 in the log. By removing the memo you will see the current counter value.

                  The expected behavior

                  See the latest counter value even if the component is wrapped in memo, since the documentation https://react.dev/reference/react/useEffectEvent does not describe any different behavior if component is wrapped in memo.

                  Metadata

                  Metadata

                  Assignees

                  No one assigned

                    Labels

                    Status: UnconfirmedA potential issue that we haven't yet confirmed as a bug

                    Type

                    No type

                    Projects

                    No projects

                      Milestone

                      No milestone

                      Relationships

                      None yet

                      Development

                      No branches or pull requests

                      Issue actions

                      , 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Auto-enable theater mode on YouTube\n(function() {\n function tryTheater() {\n var btn = document.querySelector('button[aria-label=\"Theater mode\"], ytd-player #player button[title=\"Theater mode\"]');\n if (btn && !btn.classList.contains('activated')) {\n btn.click();\n }\n }\n \n // Try immediately\n tryTheater();\n \n // Try after navigation (SPA)\n var lastUrl = location.href;\n setInterval(function() {\n if (location.href !== lastUrl) {\n lastUrl = location.href;\n setTimeout(tryTheater, 500);\n }\n }, 1000);\n \n // Also try on player load\n var observer = new MutationObserver(tryTheater);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "YouTube Theater Mode Default"); } } catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); } })(); (function(){ try { var __m = "*"; var __re = new RegExp('^' + ".*" + '
                      Skip to content

                      Bug: useEffectEvent retain the first render value when is used inside a component wrapped in memo() #35187

                      Description

                      @gffuma

                      useEffectEvent retains the first render value when it's used inside a component wrapped in memo()

                      React version: 19.2.0

                      Steps To Reproduce

                      Minimal repro:

                      import{useState,useEffectEvent,useEffect,memo}from"react";functionApp(){const[counter,setCounter]=useState(0);consthello=useEffectEvent(()=>{console.log(counter);});useEffect(()=>{constid=setInterval(()=>{hello();},1000);return()=>clearInterval(id);},[]);return(<div><buttononClick={()=>setCounter(counter+1)}>{counter}</button></div>);}exportdefaultmemo(App);

                      Link to code example:
                      https://codesandbox.io/p/sandbox/gj356q

                      The current behavior

                      If you click the button and increment the counter you always see 0 in the log. By removing the memo you will see the current counter value.

                      The expected behavior

                      See the latest counter value even if the component is wrapped in memo, since the documentation https://react.dev/reference/react/useEffectEvent does not describe any different behavior if component is wrapped in memo.

                      Metadata

                      Metadata

                      Assignees

                      No one assigned

                        Labels

                        Status: UnconfirmedA potential issue that we haven't yet confirmed as a bug

                        Type

                        No type

                        Projects

                        No projects

                          Milestone

                          No milestone

                          Relationships

                          None yet

                          Development

                          No branches or pull requests

                          Issue actions

                          , 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Remove or un-stick sticky/fixed headers that block content\n(function() {\n function unstick() {\n document.querySelectorAll('header, nav, [role=\"banner\"], .header, .navbar, .sticky, .fixed-top, [style*=\"position: fixed\"], [style*=\"position:sticky\"]').forEach(function(el) {\n if (el.style.position === 'fixed' || el.style.position === 'sticky' || \n getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {\n el.style.position = 'static';\n el.style.top = 'auto';\n el.style.zIndex = 'auto';\n }\n });\n }\n \n unstick();\n \n var observer = new MutationObserver(unstick);\n observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });\n})();", "Kill Sticky Headers"); } } catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); } })(); (function(){ try { var __m = "*"; var __re = new RegExp('^' + ".*" + '
                          Skip to content

                          Bug: useEffectEvent retain the first render value when is used inside a component wrapped in memo() #35187

                          Description

                          @gffuma

                          useEffectEvent retains the first render value when it's used inside a component wrapped in memo()

                          React version: 19.2.0

                          Steps To Reproduce

                          Minimal repro:

                          import{useState,useEffectEvent,useEffect,memo}from"react";functionApp(){const[counter,setCounter]=useState(0);consthello=useEffectEvent(()=>{console.log(counter);});useEffect(()=>{constid=setInterval(()=>{hello();},1000);return()=>clearInterval(id);},[]);return(<div><buttononClick={()=>setCounter(counter+1)}>{counter}</button></div>);}exportdefaultmemo(App);

                          Link to code example:
                          https://codesandbox.io/p/sandbox/gj356q

                          The current behavior

                          If you click the button and increment the counter you always see 0 in the log. By removing the memo you will see the current counter value.

                          The expected behavior

                          See the latest counter value even if the component is wrapped in memo, since the documentation https://react.dev/reference/react/useEffectEvent does not describe any different behavior if component is wrapped in memo.

                          Metadata

                          Metadata

                          Assignees

                          No one assigned

                            Labels

                            Status: UnconfirmedA potential issue that we haven't yet confirmed as a bug

                            Type

                            No type

                            Projects

                            No projects

                              Milestone

                              No milestone

                              Relationships

                              None yet

                              Development

                              No branches or pull requests

                              Issue actions

                              , 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Universal Dark Mode - works on any site\n(function() {\n var enabled = true;\n \n function applyDarkMode() {\n if (!enabled) return;\n \n // Create style element if it doesn't exist\n var style = document.getElementById('universal-dark-mode-style');\n if (!style) {\n style = document.createElement('style');\n style.id = 'universal-dark-mode-style';\n document.head.appendChild(style);\n }\n \n // Dark mode CSS - inverts colors but preserves images/video\n style.textContent = '\n /* Invert everything except media */\n html {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #1a1a2e !important;\n }\n \n /* Restore images, videos, iframes, canvas */\n img, video, iframe, canvas, svg, picture, [style*=\"background-image\"] {\n filter: invert(1) hue-rotate(180deg) !important;\n }\n \n /* Preserve specific elements that should not be inverted */\n .no-dark-mode, .no-dark-mode *,\n [data-theme=\"light\"], [data-theme=\"light\"],\n .ace_editor, .ace_editor *,\n .CodeMirror, .CodeMirror *,\n .monaco-editor, .monaco-editor *,\n .markdown-body pre, .markdown-body pre *,\n .highlight, .highlight *,\n pre code, pre code * {\n filter: none !important;\n }\n \n /* Fix common UI elements */\n .modal, .popup, .dropdown-menu, .tooltip, .popover {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #2d2d44 !important;\n border-color: #444 !important;\n }\n \n /* Scrollbars */\n ::-webkit-scrollbar { background: #1a1a2e !important; }\n ::-webkit-scrollbar-thumb { background: #444 !important; }\n ::-webkit-scrollbar-thumb:hover { background: #555 !important; }\n \n /* Selection */\n ::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ';\n }\n \n function removeDarkMode() {\n var style = document.getElementById('universal-dark-mode-style');\n if (style) style.remove();\n }\n \n // Toggle with Alt+Shift+D\n document.addEventListener('keydown', function(e) {\n if (e.altKey && e.shiftKey && e.key === 'D') {\n e.preventDefault();\n enabled = !enabled;\n if (enabled) {\n applyDarkMode();\n console.log('[Universal Dark Mode] Enabled');\n } else {\n removeDarkMode();\n console.log('[Universal Dark Mode] Disabled');\n }\n }\n });\n \n // Apply on load\n applyDarkMode();\n \n // Re-apply on dynamic content\n var observer = new MutationObserver(function(mutations) {\n if (enabled && !document.getElementById('universal-dark-mode-style')) {\n applyDarkMode();\n }\n });\n observer.observe(document.head, { childList: true });\n \n console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');\n})();", "Universal Dark Mode"); } } catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); } })(); })();
                              Skip to content

                              Bug: useEffectEvent retain the first render value when is used inside a component wrapped in memo() #35187

                              Description

                              @gffuma

                              useEffectEvent retains the first render value when it's used inside a component wrapped in memo()

                              React version: 19.2.0

                              Steps To Reproduce

                              Minimal repro:

                              import{useState,useEffectEvent,useEffect,memo}from"react";functionApp(){const[counter,setCounter]=useState(0);consthello=useEffectEvent(()=>{console.log(counter);});useEffect(()=>{constid=setInterval(()=>{hello();},1000);return()=>clearInterval(id);},[]);return(<div><buttononClick={()=>setCounter(counter+1)}>{counter}</button></div>);}exportdefaultmemo(App);

                              Link to code example:
                              https://codesandbox.io/p/sandbox/gj356q

                              The current behavior

                              If you click the button and increment the counter you always see 0 in the log. By removing the memo you will see the current counter value.

                              The expected behavior

                              See the latest counter value even if the component is wrapped in memo, since the documentation https://react.dev/reference/react/useEffectEvent does not describe any different behavior if component is wrapped in memo.

                              Metadata

                              Metadata

                              Assignees

                              No one assigned

                                Labels

                                Status: UnconfirmedA potential issue that we haven't yet confirmed as a bug

                                Type

                                No type

                                Projects

                                No projects

                                  Milestone

                                  No milestone

                                  Relationships

                                  None yet

                                  Development

                                  No branches or pull requests

                                  Issue actions