From 2c2df5ea01eb5cd8b9ea226b2869337e59c5fe3e Mon Sep 17 00:00:00 2001 From: Florian Merz Date: Thu, 11 Feb 2021 14:50:24 +0100 Subject: unslug pt-pt: move --- .../reference/operators/function/index.html | 139 +++++++++++++++++++++ 1 file changed, 139 insertions(+) create mode 100644 files/pt-pt/web/javascript/reference/operators/function/index.html (limited to 'files/pt-pt/web/javascript/reference/operators/function') diff --git a/files/pt-pt/web/javascript/reference/operators/function/index.html b/files/pt-pt/web/javascript/reference/operators/function/index.html new file mode 100644 index 0000000000..450183b727 --- /dev/null +++ b/files/pt-pt/web/javascript/reference/operators/function/index.html @@ -0,0 +1,139 @@ +--- +title: Expressão função (Function expression) +slug: Web/JavaScript/Reference/Operadores/função +tags: + - Expressões Primárias + - Funiconaldiade de Linguagem + - Função + - JavaScript + - Operador +translation_of: Web/JavaScript/Reference/Operators/function +--- +
{{jsSidebar("Operators")}}
+ +

A palavra-chave function  pode ser utilziada para definir uma função dentro de uma expressão.

+ +

You can also define functions using the Function constructor and a function declaration.

+ +
{{EmbedInteractiveExample("pages/js/expressions-functionexpression.html", "shorter")}}
+ + + +

Sintaxe

+ +
let myFunction = function [name]([param1[, param2[, ..., paramN]]]) {
+   statements
+};
+ +

As of ES2015, you can also use {{jsxref("Functions/Arrow_functions", "arrow functions")}}.

+ +

Parâmetros

+ +
+
name {{optional_inline}}
+
The function name. Can be omitted, in which case the function is anonymous. The name is only local to the function body.
+
paramN {{optional_inline}}
+
The name of an argument to be passed to the function.
+
statements {{optional_inline}}
+
The statements which comprise the body of the function.
+
+ +

Descrição

+ +

A function expression is very similar to and has almost the same syntax as a function declaration (see {{jsxref("Statements/function", "function statement")}} for details). The main difference between a function expression and a function declaration is the function name, which can be omitted in function expressions to create anonymous functions. A function expression can be used as an IIFE (Immediately Invoked Function Expression) which runs as soon as it is defined. See also the chapter about {{jsxref("Functions", "functions")}} for more information.

+ +

Function expression hoisting

+ +

Function expressions in JavaScript are not hoisted, unlike {{jsxref("Statements/function", "function declarations", "#Function_declaration_hoisting")}}. You can't use function expressions before you define them:

+ +
console.log(notHoisted) // undefined
+//  even though the variable name is hoisted, the definition isn't. so it's undefined.
+notHoisted(); // TypeError: notHoisted is not a function
+
+var notHoisted = function() {
+   console.log('bar');
+};
+
+ +

Named function expression

+ +

If you want to refer to the current function inside the function body, you need to create a named function expression. This name is then local only to the function body (scope). This also avoids using the non-standard {{jsxref("Functions/arguments/callee", "arguments.callee")}} property.

+ +
let math = {
+  'factit': function factorial(n) {
+    console.log(n)
+    if (n <= 1) {
+      return 1;
+    }
+    return n * factorial(n - 1);
+  }
+};
+
+math.factit(3) //3;2;1;
+
+ +

The variable the function expression is assigned to will have a name property. The name doesn't change if it's assigned to a different variable. If function name is omitted, it will be the variable name (implicit name). If function name is present, it will be the function name (explicit name). This also applies to {{jsxref("Functions/Arrow_functions", "arrow functions")}} (arrows don't have a name so you can only give the variable an implicit name).

+ +
var foo = function() {}
+foo.name // "foo"
+
+var foo2 = foo
+foo2.name // "foo"
+
+var bar = function baz() {}
+bar.name // "baz"
+
+console.log(foo === foo2); // true
+console.log(typeof baz); // undefined
+console.log(bar === baz); // false (errors because baz == undefined)
+
+ +

Exemplos

+ +

The following example defines an unnamed function and assigns it to x. The function returns the square of its argument:

+ +
var x = function(y) {
+   return y * y;
+};
+
+ +

More commonly it is used as a callback:

+ +
button.addEventListener('click', function(event) {
+    console.log('button is clicked!')
+})
+ +

Especificações

+ + + + + + + + + + + + +
Especificação
{{SpecName('ESDraft', '#sec-function-definitions', 'Function definitions')}}
+ +

Compatibilidade de navegador

+ + + +

{{Compat("javascript.operators.function")}}

+ +

Consulte também 

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