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/bind/index.html | 321 +++++++++++++++++++++ 1 file changed, 321 insertions(+) create mode 100644 files/zh-tw/web/javascript/reference/global_objects/function/bind/index.html (limited to 'files/zh-tw/web/javascript/reference/global_objects/function/bind/index.html') diff --git a/files/zh-tw/web/javascript/reference/global_objects/function/bind/index.html b/files/zh-tw/web/javascript/reference/global_objects/function/bind/index.html new file mode 100644 index 0000000000..7092477133 --- /dev/null +++ b/files/zh-tw/web/javascript/reference/global_objects/function/bind/index.html @@ -0,0 +1,321 @@ +--- +title: Function.prototype.bind() +slug: Web/JavaScript/Reference/Global_Objects/Function/bind +translation_of: Web/JavaScript/Reference/Global_Objects/Function/bind +--- +
{{JSRef}}
+ +

bind() 方法，會建立一個新函式。該函式被呼叫時，會將 this 關鍵字設為給定的參數，並在呼叫時，帶有提供之前，給定順序的參數。

+ +

語法

+ +
fun.bind(thisArg[, arg1[, arg2[, ...]]])
+ +

參數

+ +
+
thisArg
+
The value to be passed as the this parameter to the target function when the bound function is called. The value is ignored if the bound function is constructed using the {{jsxref("Operators/new", "new")}} operator.
+
arg1, arg2, ...
+
Arguments to prepend to arguments provided to the bound function when invoking the target function.
+
+ +

回傳值

+ +

A copy of the given function with the specified this value and initial arguments.

+ +

敘述

+ +

bind() 函式建立了一個新的綁定函式（BF）。BF 是個包裝了原有函式物件的 exotic function object（ECMAScript 2015 的術語）。通常，呼叫 BF 會執行該 wrapped function。 BF 含有以下內部屬性：

+ + + +

When bound function is called, it calls internal method [[Call]] on [[BoundTargetFunction]], with following arguments Call(boundThis, args). Where, boundThis is [[BoundThis]], args is [[BoundArguments]] followed by the arguments passed by the function call.

+ +

A bound function may also be constructed using the new operator: doing so acts as though the target function had instead been constructed. The provided this value is ignored, while prepended arguments are provided to the emulated function.

+ +

範例

+ +

建立綁定函式

+ +

The simplest use of bind() is to make a function that, no matter how it is called, is called with a particular this value. A common mistake for new JavaScript programmers is to extract a method from an object, then to later call that function and expect it to use the original object as its this (e.g. by using that method in callback-based code). Without special care, however, the original object is usually lost. Creating a bound function from the function, using the original object, neatly solves this problem:

+ +
this.x = 9;    // this refers to global "window" object here in the browser
+var module = {
+  x: 81,
+  getX: function() { return this.x; }
+};
+
+module.getX(); // 81
+
+var retrieveX = module.getX;
+retrieveX();
+// returns 9 - The function gets invoked at the global scope
+
+// Create a new function with 'this' bound to module
+// New programmers might confuse the
+// global var x with module's property x
+var boundGetX = retrieveX.bind(module);
+boundGetX(); // 81
+
+ +

Partially applied functions

+ +

The next simplest use of bind() is to make a function with pre-specified initial arguments. These arguments (if any) follow the provided this value and are then inserted at the start of the arguments passed to the target function, followed by the arguments passed to the bound function, whenever the bound function is called.

+ +
function list() {
+  return Array.prototype.slice.call(arguments);
+}
+
+var list1 = list(1, 2, 3); // [1, 2, 3]
+
+// Create a function with a preset leading argument
+var leadingThirtysevenList = list.bind(null, 37);
+
+var list2 = leadingThirtysevenList();
+// [37]
+
+var list3 = leadingThirtysevenList(1, 2, 3);
+// [37, 1, 2, 3]
+
+ +

配合 setTimeout

+ +

By default within {{domxref("window.setTimeout()")}}, the this keyword will be set to the {{ domxref("window") }} (or global) object. When working with class methods that require this to refer to class instances, you may explicitly bind this to the callback function, in order to maintain the instance.

+ +
function LateBloomer() {
+  this.petalCount = Math.floor(Math.random() * 12) + 1;
+}
+
+// Declare bloom after a delay of 1 second
+LateBloomer.prototype.bloom = function() {
+  window.setTimeout(this.declare.bind(this), 1000);
+};
+
+LateBloomer.prototype.declare = function() {
+  console.log('I am a beautiful flower with ' +
+    this.petalCount + ' petals!');
+};
+
+var flower = new LateBloomer();
+flower.bloom();
+// after 1 second, triggers the 'declare' method
+ +

Bound functions used as constructors

+ +
+

Warning: This section demonstrates JavaScript capabilities and documents some edge cases of the bind() method. The methods shown below are not the best way to do things and probably should not be used in any production environment.

+
+ +

Bound functions are automatically suitable for use with the {{jsxref("Operators/new", "new")}} operator to construct new instances created by the target function. When a bound function is used to construct a value, the provided this is ignored. However, provided arguments are still prepended to the constructor call:

+ +
function Point(x, y) {
+  this.x = x;
+  this.y = y;
+}
+
+Point.prototype.toString = function() {
+  return this.x + ',' + this.y;
+};
+
+var p = new Point(1, 2);
+p.toString(); // '1,2'
+
+// not supported in the polyfill below,
+
+// works fine with native bind:
+
+var YAxisPoint = Point.bind(null, 0/*x*/);
+
+
+var emptyObj = {};
+var YAxisPoint = Point.bind(emptyObj, 0/*x*/);
+
+var axisPoint = new YAxisPoint(5);
+axisPoint.toString(); // '0,5'
+
+axisPoint instanceof Point; // true
+axisPoint instanceof YAxisPoint; // true
+new Point(17, 42) instanceof YAxisPoint; // true
+
+ +

Note that you need do nothing special to create a bound function for use with {{jsxref("Operators/new", "new")}}. The corollary is that you need do nothing special to create a bound function to be called plainly, even if you would rather require the bound function to only be called using {{jsxref("Operators/new", "new")}}.

+ +
// Example can be run directly in your JavaScript console
+// ...continuing from above
+
+// Can still be called as a normal function
+// (although usually this is undesired)
+YAxisPoint(13);
+
+emptyObj.x + ',' + emptyObj.y;
+// >  '0,13'
+
+ +

If you wish to support the use of a bound function only using {{jsxref("Operators/new", "new")}}, or only by calling it, the target function must enforce that restriction.

+ +

Creating shortcuts

+ +

bind() is also helpful in cases where you want to create a shortcut to a function which requires a specific this value.

+ +

Take {{jsxref("Array.prototype.slice")}}, for example, which you want to use for converting an array-like object to a real array. You could create a shortcut like this:

+ +
var slice = Array.prototype.slice;
+
+// ...
+
+slice.apply(arguments);
+
+ +

With bind(), this can be simplified. In the following piece of code, slice is a bound function to the {{jsxref("Function.prototype.apply()", "apply()")}} function of {{jsxref("Function.prototype")}}, with the this value set to the {{jsxref("Array.prototype.slice()", "slice()")}} function of {{jsxref("Array.prototype")}}. This means that additional apply() calls can be eliminated:

+ +
// same as "slice" in the previous example
+var unboundSlice = Array.prototype.slice;
+var slice = Function.prototype.apply.bind(unboundSlice);
+
+// ...
+
+slice(arguments);
+
+ +

Polyfill

+ +

You can partially work around this by inserting the following code at the beginning of your scripts, allowing use of much of the functionality of bind() in implementations that do not natively support it.

+ +
if (!Function.prototype.bind) {
+  Function.prototype.bind = function(oThis) {
+    if (typeof this !== 'function') {
+      // closest thing possible to the ECMAScript 5
+      // internal IsCallable function
+      throw new TypeError('Function.prototype.bind - what is trying to be bound is not callable');
+    }
+
+    var aArgs   = Array.prototype.slice.call(arguments, 1),
+        fToBind = this,
+        fNOP    = function() {},
+        fBound  = function() {
+          return fToBind.apply(this instanceof fNOP
+                 ? this
+                 : oThis,
+                 aArgs.concat(Array.prototype.slice.call(arguments)));
+        };
+
+    if (this.prototype) {
+      // Function.prototype doesn't have a prototype property
+      fNOP.prototype = this.prototype;
+    }
+    fBound.prototype = new fNOP();
+
+    return fBound;
+  };
+}
+
+ +

Some of the many differences (there may well be others, as this list does not seriously attempt to be exhaustive) between this algorithm and the specified algorithm are:

+ + + +

If you choose to use this partial implementation, you must not rely on those cases where behavior deviates from ECMA-262, 5th edition! With some care, however (and perhaps with additional modification to suit specific needs), this partial implementation may be a reasonable bridge to the time when bind() is widely implemented according to the specification.

+ +

Please check https://github.com/Raynos/function-bind for a more thorough solution!

+ +

規範

+ + + + + + + + + + + + + + + + + + + + + + + + +
SpecificationStatusComment
{{SpecName('ES5.1', '#sec-15.3.4.5', 'Function.prototype.bind')}}{{Spec2('ES5.1')}}Initial definition. Implemented in JavaScript 1.8.5.
{{SpecName('ES2015', '#sec-function.prototype.bind', 'Function.prototype.bind')}}{{Spec2('ES2015')}} 
{{SpecName('ESDraft', '#sec-function.prototype.bind', 'Function.prototype.bind')}}{{Spec2('ESDraft')}} 
+ +

瀏覽器相容性

+ +
{{CompatibilityTable}}
+ +
+ + + + + + + + + + + + + + + + + + + + + +
FeatureChromeEdgeFirefox (Gecko)Internet ExplorerOperaSafari
Basic support{{CompatChrome("7")}}{{CompatVersionUnknown}}{{CompatGeckoDesktop("2")}}{{CompatIE("9")}}{{CompatOpera("11.60")}}{{CompatSafari("5.1")}}
+
+ +
+ + + + + + + + + + + + + + + + + + + + + + + +
FeatureAndroidChrome for AndroidEdgeFirefox Mobile (Gecko)IE MobileOpera MobileSafari Mobile
Basic support{{CompatAndroid("4.0")}}{{CompatChrome("1")}}{{CompatVersionUnknown}}{{CompatGeckoMobile("2")}}{{CompatUnknown}}{{CompatOperaMobile("11.5")}}{{CompatSafari("6.0")}}
+
+ +

相關連結

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