From 218934fa2ed1c702a6d3923d2aa2cc6b43c48684 Mon Sep 17 00:00:00 2001 From: Peter Bengtsson Date: Tue, 8 Dec 2020 14:43:23 -0500 Subject: initial commit --- .../global_objects/function/length/index.html | 144 +++++++++++++++++++++ 1 file changed, 144 insertions(+) create mode 100644 files/zh-tw/web/javascript/reference/global_objects/function/length/index.html (limited to 'files/zh-tw/web/javascript/reference/global_objects/function/length') diff --git a/files/zh-tw/web/javascript/reference/global_objects/function/length/index.html b/files/zh-tw/web/javascript/reference/global_objects/function/length/index.html new file mode 100644 index 0000000000..699e1ff178 --- /dev/null +++ b/files/zh-tw/web/javascript/reference/global_objects/function/length/index.html @@ -0,0 +1,144 @@ +--- +title: Function.length +slug: Web/JavaScript/Reference/Global_Objects/Function/length +translation_of: Web/JavaScript/Reference/Global_Objects/Function/length +--- +
{{JSRef}}
+ +

length property表示該 function 預期被傳入的參數數量

+ +
{{js_property_attributes(0,0,1)}}
+ +

描述

+ +

length 是 function 物件的一個 property，表示該 function 預期被傳入的參數數量，這個數量並不包含 {{jsxref("rest_parameters", "rest parameter", "", 1)}} 且只包涵第一個預設參數(Default Parameters)前的參數。相較之下 {{jsxref("Functions_and_function_scope/arguments/length", "arguments.length")}} 是 function 內部的物件，會提供真正傳進 function 中的參數數量。

+ +

Function 建構子的 data property

+ +

{{jsxref("Function")}} 建構子本身就是一個 {{jsxref("Function")}} 物件。其 length data property 的值為 1。此 property 的 attributes 包含: Writable: false, Enumerable: false, Configurable: true.

+ +

Function prototype 物件的 property

+ +

{{jsxref("Function")}} prototype 物件的 length property 其值為 0。

+ +

範例

+ +
console.log(Function.length); /* 1 */
+
+console.log((function()        {}).length); /* 0 */
+console.log((function(a)       {}).length); /* 1 */
+console.log((function(a, b)    {}).length); /* 2 以此類推. */
+
+console.log((function(...args) {}).length); /* 0, rest parameter 不包含在內 */
+
+console.log((function(a, b = 1, c) {}).length); /* 1 */
+// 只有在預設參數前的參數會被算到，也就是只有 a 會被視為必須傳入的參數
+// 而 c 將被預設為 undefined
+
+ +

規範

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
規範狀態註釋
{{SpecName('ES1')}}{{Spec2('ES1')}}最初的定義，在 JavaScript 1.1 中實作。
{{SpecName('ES5.1', '#sec-15.3.5.1', 'Function.length')}}{{Spec2('ES5.1')}} 
{{SpecName('ES6', '#sec-function-instances-length', 'Function.length')}}{{Spec2('ES6')}}此 property 的 configurable attribute 現在為 true.
{{SpecName('ESDraft', '#sec-function-instances-length', 'Function.length')}}{{Spec2('ESDraft')}} 
+ +

瀏覽器相容性

+ +
{{CompatibilityTable}}
+ +
+ + + + + + + + + + + + + + + + + + + + + + + + + + + +
特點ChromeFirefox (Gecko)Internet ExplorerOperaSafari
Basic support{{CompatVersionUnknown}}{{CompatVersionUnknown}}{{CompatVersionUnknown}}{{CompatVersionUnknown}}{{CompatVersionUnknown}}
Configurable: true{{CompatUnknown}}{{CompatGeckoDesktop(37)}}{{CompatUnknown}}{{CompatUnknown}}{{CompatUnknown}}
+
+ +
+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
FeatureAndroidChrome for AndroidFirefox Mobile (Gecko)IE MobileOpera MobileSafari Mobile
Basic support{{CompatVersionUnknown}}{{CompatVersionUnknown}}{{CompatVersionUnknown}}{{CompatVersionUnknown}}{{CompatVersionUnknown}}{{CompatVersionUnknown}}
Configurable: true{{CompatUnknown}}{{CompatUnknown}}{{CompatGeckoMobile(37)}}{{CompatUnknown}}{{CompatUnknown}}{{CompatUnknown}}
+
+ +

可參閱

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