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+---
+title: 'TypeError: can''t access property "x" of "y"'
+slug: Web/JavaScript/Reference/Errors/Cant_access_property
+tags:
+  - Erros
+  - JavaScript
+  - TypeError
+translation_of: Web/JavaScript/Reference/Errors/Cant_access_property
+---
+<div>{{jsSidebar("Errors")}}</div>
+
+<h2 id="Mensagem">Mensagem</h2>
+
+<pre class="syntaxbox">TypeError: Unable to get property {x} of undefined or null reference (Edge)
+TypeError: can't access property {x} of {y} (Firefox)
+TypeError: {y} is undefined, can't access property {x} of it (Firefox)
+TypeError: {y} is null, can't access property {x} of it (Firefox)
+
+Exemplos:
+TypeError: x is undefined, can't access property "prop" of it
+TypeError: x is null, can't access property "prop" of it
+TypeError: can't access property "prop" of undefined
+TypeError: can't access property "prop" of null
+</pre>
+
+<h2 id="Tipo_de_Erro">Tipo de Erro</h2>
+
+<p>{{jsxref("TypeError")}}.</p>
+
+<h2 id="O_que_deu_errado">O que deu errado?</h2>
+
+<p>O acesso a propriedade foi realizado com um valor {{jsxref("undefined")}} ou {{jsxref("null")}}.</p>
+
+<h2 id="Exemplos">Exemplos</h2>
+
+<h3 id="Casos_inválidos">Casos inválidos</h3>
+
+<pre class="brush: js example-bad">// casos undefined e null, onde o metódo substring não irá funcionar
+
+var foo = undefined;
+foo.substring(1); // TypeError: x is undefined, can't access property "substring" of it
+
+var foo = null;
+foo.substring(1); // TypeError: x is null, can't access property "substring" of it
+</pre>
+
+<h3 id="Corrigindo_o_problema">Corrigindo o problema</h3>
+
+<p>Para corrigir o problema de valores <code>undefined</code> ou <code>null</code>,  você pode usar o operador <a href="/en-US/docs/Web/JavaScript/Reference/Operators/typeof">typeof</a>, como no exemplo abaixo.</p>
+
+<pre class="brush: js">if (typeof foo !== 'undefined') {
+  // Agora que sabemos que <em>foo</em> está definida, podemos prosseguir
+}</pre>
+
+<h2 id="Veja_também">Veja também</h2>
+
+<ul>
+ <li>{{jsxref("undefined")}}</li>
+ <li>{{jsxref("null")}}</li>
+</ul>