{"id":59409,"date":"2023-10-09T23:03:47","date_gmt":"2023-10-10T02:03:47","guid":{"rendered":"https:\/\/kinsta.com\/pt\/?p=59409&post_type=knowledgebase&preview_id=59409"},"modified":"2025-10-01T17:01:13","modified_gmt":"2025-10-01T20:01:13","slug":"typeerror-cannot-read-property-map-of-undefined","status":"publish","type":"post","link":"https:\/\/kinsta.com\/pt\/blog\/typeerror-cannot-read-property-map-of-undefined\/","title":{"rendered":"Como Corrigir o Erro “TypeError: Cannot Read Property ‘Map’ of Undefined” no React"},"content":{"rendered":"

Voc\u00ea est\u00e1 se deparando com o frustrante erro “TypeError: Cannot Read Property ‘Map’ of Undefined” em seu aplicativo React<\/a>? Este erro pode ser complicado de depurar, mas n\u00e3o se preocupe \u2013 estamos aqui para ajudar.<\/p>\n

Neste artigo, mostraremos a voc\u00ea as causas e solu\u00e7\u00f5es comuns para ajud\u00e1-lo a corrigir esse erro. Independentemente de voc\u00ea ser um desenvolvedor React<\/a> experiente ou estar apenas come\u00e7ando, este guia ajudar\u00e1 voc\u00ea a colocar seu aplicativo de volta nos trilhos.
\n

<\/div><\/kinsta-auto-toc><\/p>\n

O que causa o erro “TypeError: Cannot Read Property ‘Map’ of Undefined”?<\/h2>\n

O erro “TypeError: Cannot Read Property ‘Map’ of Undefined” geralmente ocorre quando voc\u00ea tenta acessar uma propriedade ou m\u00e9todo de um valor indefinido no c\u00f3digo React.<\/p>\n

Em termos simples, o erro ocorre quando voc\u00ea tenta mapear um valor indefinido, como uma array que n\u00e3o foi inicializada ou que ainda n\u00e3o recebeu dados.<\/p>\n

No exemplo abaixo, voc\u00ea est\u00e1 obtendo itens de tarefas do JSON Placeholder<\/a>, mas o m\u00e9todo map \u00e9 chamado antes que os dados de uma solicita\u00e7\u00e3o de API<\/a> tenham chegado.<\/p>\n

import { useState, useEffect } from 'react';\n\nfunction App() {\n  const [todos, setTodos] = useState();\n\n  useEffect(() => {\n    const getTodos = async () => {\n      const response = await fetch(\n        'https:\/\/jsonplaceholder.typicode.com\/todos?_limit=5'\n      );\n      const data = await response.json();\n      setTodos(data);\n    };\n    getTodos();\n  }, []);\n\n  console.log(todos);\n\n  return (\n    <div>\n      {todos.map((todo) => (\n        <div key={todo.id}>\n          <h2>Item: {todo.title}<\/h2>\n        <\/div>\n      ))}\n    <\/div>\n  );\n}\n\nexport default App;<\/code><\/pre>\n
O c\u00f3digo acima lan\u00e7ar\u00e1 a mensagem “TypeError: Cannot read properties of undefined (reading ‘map’)”:<\/p>\n
\"TypeError:
TypeError: Cannot read properties of undefined (reading ‘map’)<\/figcaption><\/figure>\n
Voc\u00ea precisa procurar uma maneira de permitir que o React<\/a> saiba que o estado de todos \u00e9 uma array, mesmo antes da array ser preenchida, ou precisa evitar que o m\u00e9todo map seja executado at\u00e9 que a vari\u00e1vel de estado de todos obtenha seus dados da solicita\u00e7\u00e3o de API.<\/p>\n\n
3 maneiras de corrigir o erro “TypeError: Cannot Read Property ‘Map’ of Undefined”<\/h2>\n
Aqui est\u00e3o tr\u00eas maneiras de corrigir o erro “TypeError: Cannot Read Property ‘Map’ of Undefined” no React:<\/p>\n
    \n
  1. Inicialize sua vari\u00e1vel de estado em um array vazio<\/li>\n
  2. Use operadores de compara\u00e7\u00e3o<\/li>\n
  3. Use o operador de encadeamento opcional (?.)<\/li>\n<\/ol>\n
    Vamos explorar cada uma dessas solu\u00e7\u00f5es e como elas podem ajudar voc\u00ea a resolver o erro em seu c\u00f3digo React.<\/p>\n
    1. Inicialize sua vari\u00e1vel de estado em um array vazio<\/h3>\n
    Uma das solu\u00e7\u00f5es diretas para o erro “TypeError: Cannot Read Property \u2018Map\u2019 of Undefined” \u00e9 garantir que a vari\u00e1vel de array que voc\u00ea est\u00e1 tentando mapear esteja definida.<\/p>\n
    Voc\u00ea pode inicializar sua vari\u00e1vel de estado com um array vazio por padr\u00e3o, o que garantir\u00e1 que a vari\u00e1vel sempre exista e n\u00e3o gere um erro quando voc\u00ea tentar mape\u00e1-la.<\/p>\n
    Por exemplo, a seguir est\u00e3o dois componentes semelhantes, a vari\u00e1vel de estado do primeiro n\u00e3o \u00e9 inicializada com um array vazio, enquanto a do segundo \u00e9 inicializada:<\/p>\n
    \/\/ Before initializing your state variable to an empty array\nfunction MyComponent() {\n  const [myList, setMyList] = useState();\n  \n  return (\n    <ul>\n      {myList.map(item => <li>{item}<\/li>)}\n    <\/ul>\n  );\n}\n\n\/\/ After initializing your state variable to an empty array\nfunction MyComponent() {\n  const [myList, setMyList] = useState([]);\n\n  return (\n    <ul>\n      {myList.map(item => <li>{item}<\/li>)}\n    <\/ul>\n  );\n}<\/code><\/pre>\n
    No exemplo acima, a vari\u00e1vel de estado myList<\/code> \u00e9 inicializada em uma array vazia por padr\u00e3o usando useState([])<\/code>. Isso garante que, mesmo que myList<\/code> seja indefinido inicialmente, ele sempre ser\u00e1 uma array e n\u00e3o lan\u00e7ar\u00e1 a mensagem “TypeError: Cannot Read Property ‘Map’ of Undefined”.<\/p>\n
    Para o exemplo de busca, voc\u00ea tamb\u00e9m pode inicializar a vari\u00e1vel de estado todos<\/code> como uma array vazia ([]<\/code>):<\/p>\n
    import { useState, useEffect } from 'react';\n\nfunction App() {\n  \/\/ Initialize the state to an empty array of todos.\n  const [todos, setTodos] = useState([]);\n\n  useEffect(() => {\n    const getTodos = async () => {\n      const response = await fetch(\n        'https:\/\/jsonplaceholder.typicode.com\/todos?_limit=5'\n      );\n      const data = await response.json();\n      setTodos(data);\n    };\n    getTodos();\n  }, []);\n\n  console.log(todos);\n\n  return (\n    <div>\n      {todos.map((todo) => (\n        <div key={todo.id}>\n          <h2>Item: {todo.title}<\/h2>\n       <\/div>\n      ))}\n    <\/div>\n  );\n}\n\nexport default App;<\/code><\/pre>\n
    2. Use operadores de compara\u00e7\u00e3o<\/h3>\n
    Outra solu\u00e7\u00e3o \u00e9 usar operadores de compara\u00e7\u00e3o para verificar se a vari\u00e1vel de array est\u00e1 definida antes de fazer o mapeamento sobre ela. Voc\u00ea pode usar o operador tern\u00e1rio ou l\u00f3gico AND (&&) para fazer isso.<\/p>\n
    Aqui est\u00e3o alguns exemplos de uso do operador tern\u00e1rio<\/em>:<\/p>\n
    function MyComponent() {\n  const [myList, setMyList] = useState();\n\n  return (\n    <ul>\n      {myList ? myList.map(item => <li>{item}<\/li>) : null}\n    <\/ul>\n  );\n}<\/code><\/pre>\n
    Neste exemplo, voc\u00ea est\u00e1 verificando se a vari\u00e1vel de array myList<\/code> est\u00e1 definida antes de tentar mape\u00e1-la. Se myList<\/code> for indefinida, o operador tern\u00e1rio retornar\u00e1 null e nada ser\u00e1 renderizado. Se myList<\/code> estiver definida, a fun\u00e7\u00e3o map ser\u00e1 chamada e os itens da lista ser\u00e3o renderizados.<\/p>\n
    Isso \u00e9 semelhante ao uso do operador l\u00f3gico AND:<\/p>\n
    function MyComponent() {\n  const [myList, setMyList] = useState();\n\n  return (\n    <ul>\n      {myList && myList.map(item => <li>{item}<\/li>)}\n    <\/ul>\n  );\n}<\/code><\/pre>\n
    Com o uso de operadores de compara\u00e7\u00e3o, como o operador tern\u00e1rio, voc\u00ea pode lidar com o carregamento, de modo que outra coisa seja exibida na tela enquanto voc\u00ea conduz os dados da API:<\/p>\n
    import { useState, useEffect } from 'react';\n\nfunction App() {\n  const [todos, setTodos] = useState();\n\n  useEffect(() => {\n    const getTodos = async () => {\n      const response = await fetch(\n        'https:\/\/jsonplaceholder.typicode.com\/todos?_limit=5'\n      );\n      const data = await response.json();\n      setTodos(data);\n    };\n    getTodos();\n  }, []);\n\n  console.log(todos);\n\n  return (\n   <div>\n      {todos ? (\n        todos.map((todo) => (\n          <div key={todo.id}>\n            <h2>Item: {todo.title}<\/h2>\n          <\/div>\n        ))\n      ) : (\n        <h1>Loading...<\/h1>\n      )}\n    <\/div>\n  );\n}\n\nexport default App;<\/code><\/pre>\n
    3. Use o operador de encadeamento opcional (?.)<\/h3>\n
    Voc\u00ea tamb\u00e9m pode usar o operador de encadeamento opcional (?.) introduzido no ES2020. Esse operador permite que voc\u00ea acesse com seguran\u00e7a propriedades ou m\u00e9todos, como o m\u00e9todo map de uma array, sem gerar um erro se o array estiver indefinido.<\/p>\n
    Aqui est\u00e1 um exemplo de um componente funcional que usa o operador de encadeamento para verificar a vari\u00e1vel de estado myList<\/code>:<\/p>\n
    function MyComponent() {\n  const [myList, setMyList] = useState();\n\n  return (\n    <div>\n      {myList?.map((item) => (\n        <p>{item}<\/p>\n      ))}\n    <\/div>\n  );\n}<\/code><\/pre>\n
    No exemplo acima, voc\u00ea est\u00e1 usando o operador de encadeamento opcional para acessar a vari\u00e1vel de array myList<\/code> com seguran\u00e7a. Se myList<\/code> for indefinido, nada ser\u00e1 renderizado. Se myList<\/code> estiver definido, o m\u00e9todo map ser\u00e1 chamado e os itens da lista ser\u00e3o renderizados.<\/p>\n\n
    Resumo<\/h2>\n
    O erro “TypeError: Cannot Read Property ‘Map’ of Undefined” pode ocorrer no React quando voc\u00ea usa o m\u00e9todo map em um valor indefinido ou nulo.<\/p>\n
    Para corrigir esse erro, discutimos tr\u00eas solu\u00e7\u00f5es. No entanto, o uso de operadores de compara\u00e7\u00e3o \u00e9 a solu\u00e7\u00e3o mais vers\u00e1til porque pode lidar com situa\u00e7\u00f5es em que sua API pode enviar uma resposta vazia ou um valor nulo.<\/p>\n
    Al\u00e9m disso, quando n\u00e3o tiver certeza se os dados que voc\u00ea receber\u00e1 ser\u00e3o um array, voc\u00ea pode adicionar alguns m\u00e9todos para verificar e converter o tipo de dados antes de chamar o m\u00e9todo map.<\/p>\n
    Confira a hospedagem de aplicativos<\/a> da Kinsta e crie seu pr\u00f3ximo projeto React<\/a> hoje mesmo!<\/p>\n
    \n
    \n
    \n
    \n
    \n
    \n
    \n
    \n
    Agora \u00e9 a sua vez: Voc\u00ea j\u00e1 encontrou esse problema? Como voc\u00ea o resolveu? Existem outras abordagens que voc\u00ea usou e que n\u00e3o foram abordadas neste artigo? Conte-nos na se\u00e7\u00e3o de coment\u00e1rios!<\/em><\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"
    Voc\u00ea est\u00e1 se deparando com o frustrante erro “TypeError: Cannot Read Property ‘Map’ of Undefined” em seu aplicativo React? Este erro pode ser complicado de depurar, …<\/p>\n","protected":false},"author":287,"featured_media":59410,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_kinsta_gated_content":false,"_kinsta_gated_content_redirect":"","footnotes":""},"tags":[],"topic":[1003,1002],"class_list":["post-59409","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","topic-erros-do-react","topic-react"],"yoast_head":"\nComo Corrigir o Erro "TypeError: Cannot Read Property 'Map' of Undefined" no React - Kinsta\u00ae<\/title>\n<meta name=\"description\" content=\"O frustrante erro "TypeError: Cannot Read Property 'Map' of Undefined" pode ser dif\u00edcil de depurar. 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