diff options
Diffstat (limited to 'files/pt-pt/web/javascript/reference/functions/rest_parameters/index.html')
| -rw-r--r-- | files/pt-pt/web/javascript/reference/functions/rest_parameters/index.html | 235 |
1 files changed, 0 insertions, 235 deletions
diff --git a/files/pt-pt/web/javascript/reference/functions/rest_parameters/index.html b/files/pt-pt/web/javascript/reference/functions/rest_parameters/index.html deleted file mode 100644 index 357ce41efa..0000000000 --- a/files/pt-pt/web/javascript/reference/functions/rest_parameters/index.html +++ /dev/null @@ -1,235 +0,0 @@ ---- -title: Parâmetros Rest -slug: Web/JavaScript/Reference/Functions/rest_parameters -tags: - - Funcionalidade Linguagem - - Funções - - JavaScript - - Parametros Rest - - Rest -translation_of: Web/JavaScript/Reference/Functions/rest_parameters -original_slug: Web/JavaScript/Reference/Funcoes/parametros_rest ---- -<div>Parâmetrois {{jsSidebar("Functions")}}</div> - -<p><span class="seoSummary">A sintaxe do <strong>parâmetro "rest"</strong> permite-nos representar um número indefinido de argumentos</span><span class="seoSummary">como um <em>array</em>.</span></p> - -<div>{{EmbedInteractiveExample("pages/js/functions-restparameters.html")}}</div> - - - -<h2 id="Sintaxe">Sintaxe</h2> - -<pre class="syntaxbox">function f(<var>a</var>, <var>b</var>, ...<var>theArgs</var>) { - // ... -}</pre> - -<h2 id="Descrição">Descrição</h2> - -<p>A function's last parameter can be prefixed with <code>...</code> which will cause all remaining (user supplied) arguments to be placed within a "standard" Javascript array.</p> - -<p>Only the last parameter can be a "rest parameter".</p> - -<pre class="brush: js">function myFun(<var>a</var>, <var>b</var>, ...<var>manyMoreArgs</var>) { - console.log("a", a) - console.log("b", b) - console.log("manyMoreArgs", manyMoreArgs) -} - -myFun("one", "two", "three", "four", "five", "six") - -// Console Output: -// a, one -// b, two -// manyMoreArgs, [three, four, five, six] -</pre> - -<h3 id="Difference_between_rest_parameters_and_the_arguments_object">Difference between rest parameters and the <code>arguments</code> object</h3> - -<p>There are three main differences between rest parameters and the {{jsxref("Functions/arguments", "arguments")}} object:</p> - -<ul> - <li>rest parameters are only the ones that haven't been given a separate name (i.e. formally defined in function expression), while the <code>arguments</code> object contains <em>all</em> arguments passed to the function;</li> - <li>the <code>arguments</code> object is not a real array, while rest parameters are {{jsxref("Global_Objects/Array", "Array")}} instances, meaning methods like {{jsxref("Array.sort", "sort")}}, {{jsxref("Array.map", "map")}}, {{jsxref("Array.forEach", "forEach")}} or {{jsxref("Array/pop", "pop")}} can be applied on it directly;</li> - <li>the <code>arguments</code> object has additional functionality specific to itself (like the <code>callee</code> property).</li> -</ul> - -<h3 id="From_arguments_to_an_array">From arguments to an array</h3> - -<p>Rest parameters have been introduced to reduce the boilerplate code that was induced by the arguments</p> - -<pre class="brush: js">// Before rest parameters, "arguments" could be converted to a normal array using: - -function f(a, b) { - - let normalArray = Array.prototype.slice.call(arguments) - // -- or -- - let normalArray = [].slice.call(arguments) - // -- or -- - let normalArray = Array.from(arguments) - - let first = normalArray.shift() // OK, gives the first argument - let first = arguments.shift() // ERROR (arguments is not a normal array) -} - -// Now, you can easily gain access to a normal array using a rest parameter - -function f(...args) { - let normalArray = args - let first = normalArray.shift() // OK, gives the first argument -} -</pre> - -<h3 id="Destructuring_rest_parameters">Destructuring rest parameters</h3> - -<p>Rest parameters can be destructured Arrays only (though objects will soon be supported). That means that their data can be unpacked into distinct variables. (See <a href="/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment">Destructuring assignment</a>.)</p> - -<pre class="brush: js">function f(...[a, b, c]) { - return a + b + c; -} - -f(1) // NaN (b and c are undefined) -f(1, 2, 3) // 6 -f(1, 2, 3, 4) // 6 (the fourth parameter is not destructured) -</pre> - -<div class="blockIndicator note"> -<h4 id="Fixme">Fixme</h4> - -<p><s>Doing this is possible, but (afaik) there's no use-case, so it's just confusing the junior audience. The following code does exactly the same. There should at least be a note, that in theory you can do something like this, but there is no point in doing so.</s> The example is contrived, but imagine that [a, b, c] were the return value of some function. Then the utility is clear.</p> - -<p><s>Also, since <a href="/en-US/docs/Web/JavaScript/Reference/Functions/arguments">Function arguments</a> will never have named parameters (this is not Python), the statement "objects will soon be supported" is wrong. </s> The preceding example may be mixing up destructuring with rest parameters. Please see the <a href="/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment">page on destructuring assignment</a> for an example with object destructuring applied in the parameters area.</p> - -<pre class="brush: js">function f(a, b, c) { - return a + b + c -} - -f(1) // NaN (b and c are undefined) -f(1, 2, 3) // 6 -f(1, 2, 3, 4) // 6 (the fourth parameter is not ...) -</pre> -</div> - -<h2 id="Exemplos">Exemplos</h2> - -<p>In this example, the first argument is mapped to <code>a</code> and the second to <code>b</code>, so these named arguments are used like normal.</p> - -<p>However, the third argument, <code>manyMoreArgs</code>, will be an array that contains the 3<sup>rd</sup>, 4<sup>th</sup>, 5<sup>th</sup>, 6<sup>th</sup> ... <var>n</var><sup>th</sup> — as many arguments that the user includes.</p> - -<pre class="brush: js">function myFun(a, b, ...manyMoreArgs) { - console.log("a", a) - console.log("b", b) - console.log("manyMoreArgs", manyMoreArgs) -} - -myFun("one", "two", "three", "four", "five", "six") - -// a, one -// b, two -// manyMoreArgs, [three, four, five, six] -</pre> - -<p>Below... even though there is just one value, the last argument still gets put into an array.</p> - -<pre class="brush: js">// using the same function definition from example above - -myFun("one", "two", "three") - -// a, one -// b, two -// manyMoreArgs, [three]</pre> - -<p>Below, the third argument isn't provided, but <code>manyMoreArgs</code> is still an array (albeit an empty one).</p> - -<pre class="brush: js">// using the same function definition from example above - -myFun("one", "two") - -// a, one -// b, two -// manyMoreArgs, []</pre> - -<p>Since <code>theArgs</code> is an array, a count of its elements is given by the <code>length</code> property:</p> - -<pre class="brush: js">function fun1(...theArgs) { - console.log(theArgs.length) -} - -fun1() // 0 -fun1(5) // 1 -fun1(5, 6, 7) // 3 -</pre> - -<p>In the next example, a rest parameter is used to collect all parameters after the first into an array. Each one of them is then multiplied by the first parameter, and the array is returned:</p> - -<pre class="brush: js">function multiply(multiplier, ...theArgs) { - return theArgs.map(function(element) { - return multiplier * element - }) -} - -let arr = multiply(2, 1, 2, 3) -console.log(arr) // [2, 4, 6] -</pre> - -<p><code>Array</code> methods can be used on rest parameters, but not on the <code>arguments</code> object:</p> - -<pre class="brush: js">function sortRestArgs(...theArgs) { - let sortedArgs = theArgs.sort() - return sortedArgs -} - -console.log(sortRestArgs(5, 3, 7, 1)) // 1, 3, 5, 7 - -function sortArguments() { - let sortedArgs = arguments.sort() - return sortedArgs // this will never happen -} - - -console.log(sortArguments(5, 3, 7, 1)) -// throws a TypeError (arguments.sort is not a function) -</pre> - -<p>To use <code>Array</code> methods on the <code>arguments</code> object, it must be converted to a real array first.</p> - -<pre class="brush: js">function sortArguments() { - let args = Array.from(arguments) - let sortedArgs = args.sort() - return sortedArgs -} -console.log(sortArguments(5, 3, 7, 1)) // 1, 3, 5, 7 -</pre> - -<h2 id="Especificações">Especificações</h2> - -<table class="standard-table"> - <thead> - <tr> - <th scope="col">Especificação</th> - </tr> - </thead> - <tbody> - <tr> - <td>{{SpecName('ESDraft', '#sec-function-definitions', 'Function Definitions')}}</td> - </tr> - </tbody> -</table> - -<h2 id="Compatibildiade_de_navegador">Compatibildiade de navegador</h2> - - - -<p>{{Compat("javascript.functions.rest_parameters")}}</p> - -<h2 id="Consulte_também">Consulte também</h2> - -<ul> - <li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Spread_operator" title="spread operator">Spread syntax</a> (also ‘<code>...</code>’)</li> - <li><a href="/en-US/docs/Web/JavaScript/Reference/Functions/arguments" title="arguments">Arguments object</a></li> - <li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" title="Array">Array</a></li> - <li><a href="/en-US/docs/Web/JavaScript/Reference/Functions" title="Functions and function scope">Functions</a></li> - <li><a class="external" href="http://wiki.ecmascript.org/doku.php?id=harmony:rest_parameters">Original proposal at ecmascript.org</a></li> - <li><a class="external" href="http://javascriptweblog.wordpress.com/2011/01/18/javascripts-arguments-object-and-beyond/">JavaScript arguments object and beyond</a></li> - <li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment">Destructuring assignment</a></li> -</ul> |