From 218934fa2ed1c702a6d3923d2aa2cc6b43c48684 Mon Sep 17 00:00:00 2001 From: Peter Bengtsson Date: Tue, 8 Dec 2020 14:43:23 -0500 Subject: initial commit --- .../reference/statements/function_star_/index.html | 207 +++++++++++++++++++++ 1 file changed, 207 insertions(+) create mode 100644 files/zh-tw/web/javascript/reference/statements/function_star_/index.html (limited to 'files/zh-tw/web/javascript/reference/statements/function_star_') diff --git a/files/zh-tw/web/javascript/reference/statements/function_star_/index.html b/files/zh-tw/web/javascript/reference/statements/function_star_/index.html new file mode 100644 index 0000000000..11b1013537 --- /dev/null +++ b/files/zh-tw/web/javascript/reference/statements/function_star_/index.html @@ -0,0 +1,207 @@ +--- +title: function* +slug: Web/JavaScript/Reference/Statements/function* +tags: + - ECMAScript 2015 + - Function + - Iterator + - JavaScript + - Statement +translation_of: Web/JavaScript/Reference/Statements/function* +--- +
{{jsSidebar("Statements")}}
+ +

function* 宣告式（function 關鍵字後面跟著一個星號）定義了一個生成器函式（generator function），他會回傳一個{{jsxref("Global_Objects/Generator","生成器（Generator）")}}物件。

+ +
{{EmbedInteractiveExample("pages/js/statement-functionasterisk.html")}}
+ + + +
+

你可以透過 {{jsxref("GeneratorFunction")}} 建構式來定義生成器函式。

+
+ +

語法

+ +
function* name([param[, param[, ... param]]]) {
+   statements
+}
+
+ +
+
name
+
函式名稱。
+
+ +
+
param
+
要被傳入函式的引數名稱，一個函式最多可以擁有 255 個引數。
+
+ +
+
statements
+
statements 構成了函式內容的陳述式。
+
+ +

描述

+ +

生成器是可以離開後再次進入的函式。在兩次進入之間，生成器的執行狀態（變數綁定狀態）會被儲存。

+ +

呼叫生成器函式並不會讓裡面的程式碼立即執行，而是會回傳一個針對該函式的迭代器（iterator）物件。當呼叫迭代器的 next() 方法時，生成器函式將會執行到遭遇的第一個 {{jsxref("Operators/yield", "yield")}} 運算式，該運算式給定的值將從迭代器中回傳，如果是 {{jsxref("Operators/yield*", "yield*")}} 則會交給另一個生成器函式處理。next() 方法回傳一個物件，該物件有 value 屬性，包含了產生的數值，還有 done 屬性，為布林值，指出該生成器是否產出最後的數值。呼叫 next() 方法如果帶有一個參數，將會讓先前暫停的生成器函式恢復執行，以該參數值取代先前暫停的 yield 陳述式。

+ +

生成器中的 return 陳述式被執行時，會讓生成器 done 狀態為真。若有數值被返回的動作帶回，將是放在 value 傳回的。已返回的生成器不會再產生任何數值。

+ +

範例

+ +

簡單例子

+ +
function* idMaker() {
+  var index = 0;
+  while (index < index+1)
+    yield index++;
+}
+
+var gen = idMaker();
+
+console.log(gen.next().value); // 0
+console.log(gen.next().value); // 1
+console.log(gen.next().value); // 2
+console.log(gen.next().value); // 3
+// ...
+ +

yield* 的範例

+ +
function* anotherGenerator(i) {
+  yield i + 1;
+  yield i + 2;
+  yield i + 3;
+}
+
+function* generator(i) {
+  yield i;
+  yield* anotherGenerator(i);
+  yield i + 10;
+}
+
+var gen = generator(10);
+
+console.log(gen.next().value); // 10
+console.log(gen.next().value); // 11
+console.log(gen.next().value); // 12
+console.log(gen.next().value); // 13
+console.log(gen.next().value); // 20
+
+ +

傳入引數至生成器

+ +
function* logGenerator() {
+  console.log(0);
+  console.log(1, yield);
+  console.log(2, yield);
+  console.log(3, yield);
+}
+
+var gen = logGenerator();
+
+// the first call of next executes from the start of the function
+// until the first yield statement
+gen.next();             // 0
+gen.next('pretzel');    // 1 pretzel
+gen.next('california'); // 2 california
+gen.next('mayonnaise'); // 3 mayonnaise
+
+ +

生成器中的回傳陳述式

+ +
function* yieldAndReturn() {
+  yield "Y";
+  return "R";
+  yield "unreachable";
+}
+
+var gen = yieldAndReturn()
+console.log(gen.next()); // { value: "Y", done: false }
+console.log(gen.next()); // { value: "R", done: true }
+console.log(gen.next()); // { value: undefined, done: true }
+
+ +

生成器無法被建構

+ +
function* f() {}
+var obj = new f; // throws "TypeError: f is not a constructor"
+ +

以表達式定義生成器

+ +
const foo = function* () { yield 10; yield 20; };
+const bar = foo();console.log(bar.next()); // {value: 10, done: false}
+ +

 

+ +

規範

+ + + + + + + + + + + + + + + + + + + + + + + + + + +
SpecificationStatusComment
{{SpecName('ES2015', '#', 'function*')}}{{Spec2('ES2015')}}Initial definition.
{{SpecName('ES2016', '#', 'function*')}}{{Spec2('ES2016')}}Changed that generators should not have [[Construct]] trap and will throw when used with new.
{{SpecName('ESDraft', '#', 'function*')}}{{Spec2('ESDraft')}} 
+ +

瀏覽器相容性

+ +
+ + +

{{Compat("javascript.statements.generator_function")}}

+
+ +

Firefox 規範註記

+ +

Generators and iterators in Firefox versions before 26

+ +

Older Firefox versions implement an older version of the generators proposal. In the older version, generators were defined using a regular function keyword (without an asterisk) among other differences. See Legacy generator function for further information.

+ +

IteratorResult object returned instead of throwing

+ +

Starting with Gecko 29 {{geckoRelease(29)}}, the completed generator function no longer throws a {{jsxref("TypeError")}} "generator has already finished". Instead, it returns an IteratorResult object like { value: undefined, done: true } ({{bug(958951)}}).

+ +

參見

+ + -- cgit v1.2.3-54-g00ecf