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---
title: throw
slug: Web/JavaScript/Reference/Statements/throw
tags:
- Comando
- Declaração
- JavaScript
translation_of: Web/JavaScript/Reference/Statements/throw
original_slug: Web/JavaScript/Reference/Extratos_e_declarações/throw
---
<div>{{jsSidebar("Statements")}}</div>
<p>A <strong>declaração <code>throw</code> </strong>lança uma exeção definida pelo utilizador. A execução da função atual irá parar (os comandos depois de <code>throw</code> não serão executados), <span id="result_box" lang="pt"><span>e o controle será passado para o primeiro bloco <code><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/try...catch">catch</a></code> no conjunto de chamadas. Se não existir nenhum bloco <code>catch</code> entre as funções de <em>caller</em>, o programa irá terminar.</span></span></p>
<h2 id="Sintaxe">Sintaxe</h2>
<pre class="syntaxbox">expressão throw; </pre>
<dl>
<dt><code>expressão</code></dt>
<dd>A expressão para <em>throw</em>.</dd>
</dl>
<h2 id="Descrição">Descrição</h2>
<p>Use the <code>throw</code> statement to throw an exception. When you throw an exception, <code>expression</code> specifies the value of the exception. Each of the following throws an exception:</p>
<pre class="brush: js">throw 'Error2'; // generates an exception with a string value
throw 42; // generates an exception with the value 42
throw true; // generates an exception with the value true</pre>
<p>Also note that the <code>throw</code> statement is affected by <a href="/en-US/docs/Web/JavaScript/Reference/Lexical_grammar#Automatic_semicolon_insertion">automatic semicolon insertion (ASI)</a> as no line terminator between the <code>throw</code> keyword and the expression is allowed.</p>
<h2 id="Exemplos">Exemplos</h2>
<h3 id="Throw_um_objeto">Throw um objeto</h3>
<p>You can specify an object when you throw an exception. You can then reference the object's properties in the <code>catch</code> block. The following example creates an object of type <code>UserException</code> and uses it in a <code>throw</code> statement.</p>
<pre class="brush: js">function UserException(message) {
this.message = message;
this.name = 'UserException';
}
function getMonthName(mo) {
mo = mo - 1; // Adjust month number for array index (1 = Jan, 12 = Dec)
var months = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul',
'Aug', 'Sep', 'Oct', 'Nov', 'Dec'];
if (months[mo] !== undefined) {
return months[mo];
} else {
throw new UserException('InvalidMonthNo');
}
}
try {
// statements to try
var myMonth = 15; // 15 is out of bound to raise the exception
var monthName = getMonthName(myMonth);
} catch (e) {
monthName = 'unknown';
console.log(e.message, e.name); // pass exception object to err handler
}
</pre>
<h3 id="Outro_exemplo_de_throwing_um_objeto">Outro exemplo de <em>throwing</em> um objeto</h3>
<p>The following example tests an input string for a U.S. zip code. If the zip code uses an invalid format, the throw statement throws an exception by creating an object of type <code>ZipCodeFormatException</code>.</p>
<pre class="brush: js">/*
* Creates a ZipCode object.
*
* Accepted formats for a zip code are:
* 12345
* 12345-6789
* 123456789
* 12345 6789
*
* If the argument passed to the ZipCode constructor does not
* conform to one of these patterns, an exception is thrown.
*/
function ZipCode(zip) {
zip = new String(zip);
pattern = /[0-9]{5}([- ]?[0-9]{4})?/;
if (pattern.test(zip)) {
// zip code value will be the first match in the string
this.value = zip.match(pattern)[0];
this.valueOf = function() {
return this.value
};
this.toString = function() {
return String(this.value)
};
} else {
throw new ZipCodeFormatException(zip);
}
}
function ZipCodeFormatException(value) {
this.value = value;
this.message = 'does not conform to the expected format for a zip code';
this.toString = function() {
return this.value + this.message;
};
}
/*
* This could be in a script that validates address data
* for US addresses.
*/
const ZIPCODE_INVALID = -1;
const ZIPCODE_UNKNOWN_ERROR = -2;
function verifyZipCode(z) {
try {
z = new ZipCode(z);
} catch (e) {
if (e instanceof ZipCodeFormatException) {
return ZIPCODE_INVALID;
} else {
return ZIPCODE_UNKNOWN_ERROR;
}
}
return z;
}
a = verifyZipCode(95060); // returns 95060
b = verifyZipCode(9560); // returns -1
c = verifyZipCode('a'); // returns -1
d = verifyZipCode('95060'); // returns 95060
e = verifyZipCode('95060 1234'); // returns 95060 1234
</pre>
<h3 id="Rethrow_uma_exceção"><em>Rethrow</em> uma exceção</h3>
<p>You can use <code>throw</code> to rethrow an exception after you catch it. The following example catches an exception with a numeric value and rethrows it if the value is over 50. The rethrown exception propagates up to the enclosing function or to the top level so that the user sees it.</p>
<pre class="brush: js">try {
throw n; // throws an exception with a numeric value
} catch (e) {
if (e <= 50) {
// statements to handle exceptions 1-50
} else {
// cannot handle this exception, so rethrow
throw e;
}
}
</pre>
<h2 id="Especificações">Especificações</h2>
<table class="standard-table">
<tbody>
<tr>
<th scope="col">Especificação</th>
<th scope="col">Estado</th>
<th scope="col">Comentário</th>
</tr>
<tr>
<td>{{SpecName('ES3')}}</td>
<td>{{Spec2('ES3')}}</td>
<td>Initial definition. Implemented in JavaScript 1.4</td>
</tr>
<tr>
<td>{{SpecName('ES5.1', '#sec-12.13', 'throw statement')}}</td>
<td>{{Spec2('ES5.1')}}</td>
<td> </td>
</tr>
<tr>
<td>{{SpecName('ES6', '#sec-throw-statement', 'throw statement')}}</td>
<td>{{Spec2('ES6')}}</td>
<td> </td>
</tr>
<tr>
<td>{{SpecName('ESDraft', '#sec-throw-statement', 'throw statement')}}</td>
<td>{{Spec2('ESDraft')}}</td>
<td> </td>
</tr>
</tbody>
</table>
<h2 id="Compatibilidade_de_navegador">Compatibilidade de navegador</h2>
<p>{{Compat("javascript.statements.throw")}}</p>
<h2 id="Consulte_também">Consulte também</h2>
<ul>
<li><a href="/pt-PT/docs/Web/JavaScript/Reference/Extratos_e_declarações/try...catch"><code>try...catch</code></a></li>
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