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/array/includes/index.html | 175 +++++++++++++++++++++ 1 file changed, 175 insertions(+) create mode 100644 files/zh-tw/web/javascript/reference/global_objects/array/includes/index.html (limited to 'files/zh-tw/web/javascript/reference/global_objects/array/includes') diff --git a/files/zh-tw/web/javascript/reference/global_objects/array/includes/index.html b/files/zh-tw/web/javascript/reference/global_objects/array/includes/index.html new file mode 100644 index 0000000000..6d3d0e0cb2 --- /dev/null +++ b/files/zh-tw/web/javascript/reference/global_objects/array/includes/index.html @@ -0,0 +1,175 @@ +--- +title: Array.prototype.includes() +slug: Web/JavaScript/Reference/Global_Objects/Array/includes +tags: + - Array + - JavaScript + - Method + - Prototype + - Reference + - polyfill +translation_of: Web/JavaScript/Reference/Global_Objects/Array/includes +--- +
{{JSRef}}
+ +

includes() 方法會判斷陣列是否包含特定的元素，並以此來回傳 true 或 false。

+ +
{{EmbedInteractiveExample("pages/js/array-includes.html")}}
+ + + +

語法

+ +
arr.includes(searchElement[, fromIndex])
+
+ +

參數

+ +
+
searchElement
+
要搜尋的元素。
+
fromIndex {{optional_inline}}
+
要於此陣列中開始搜尋 searchElement 的位置。如為負數值，則自 array.length + fromIndex 開始向後搜尋。預設值為 0。
+
+ +

回傳值

+ +

布林值（{{jsxref("Boolean")}}）。

+ +

範例

+ +
[1, 2, 3].includes(2);     // true
+[1, 2, 3].includes(4);     // false
+[1, 2, 3].includes(3, 3);  // false
+[1, 2, 3].includes(3, -1); // true
+[1, 2, NaN].includes(NaN); // true
+
+ +

fromIndex 大於或等於陣列長度

+ +

如果 fromIndex大於或等於陣列長度, 會回傳false. 此陣列將不會被搜尋.

+ +
var arr = ['a', 'b', 'c'];
+
+arr.includes('c', 3);   // false
+arr.includes('c', 100); // false
+ +

Computed index is less than 0

+ +

If fromIndex is negative, the computed index is calculated to be used as a position in the array at which to begin searching for searchElement. If the computed index is less than 0, the entire array will be searched.

+ +
// array length is 3
+// fromIndex is -100
+// computed index is 3 + (-100) = -97
+
+var arr = ['a', 'b', 'c'];
+
+arr.includes('a', -100); // true
+arr.includes('b', -100); // true
+arr.includes('c', -100); // true
+ +

includes() used as a generic method

+ +

includes() method is intentionally generic. It does not require this value to be an Array object, so it can be applied to other kinds of objects (e.g. array-like objects). The example below illustrates includes() method called on the function's arguments object.

+ +
(function() {
+  console.log([].includes.call(arguments, 'a')); // true
+  console.log([].includes.call(arguments, 'd')); // false
+})('a','b','c');
+ +

Polyfill

+ +
// https://tc39.github.io/ecma262/#sec-array.prototype.includes
+if (!Array.prototype.includes) {
+  Object.defineProperty(Array.prototype, 'includes', {
+    value: function(searchElement, fromIndex) {
+
+      if (this == null) {
+        throw new TypeError('"this" is null or not defined');
+      }
+
+      // 1. Let O be ? ToObject(this value).
+      var o = Object(this);
+
+      // 2. Let len be ? ToLength(? Get(O, "length")).
+      var len = o.length >>> 0;
+
+      // 3. If len is 0, return false.
+      if (len === 0) {
+        return false;
+      }
+
+      // 4. Let n be ? ToInteger(fromIndex).
+      //    (If fromIndex is undefined, this step produces the value 0.)
+      var n = fromIndex | 0;
+
+      // 5. If n ≥ 0, then
+      //  a. Let k be n.
+      // 6. Else n < 0,
+      //  a. Let k be len + n.
+      //  b. If k < 0, let k be 0.
+      var k = Math.max(n >= 0 ? n : len - Math.abs(n), 0);
+
+      function sameValueZero(x, y) {
+        return x === y || (typeof x === 'number' && typeof y === 'number' && isNaN(x) && isNaN(y));
+      }
+
+      // 7. Repeat, while k < len
+      while (k < len) {
+        // a. Let elementK be the result of ? Get(O, ! ToString(k)).
+        // b. If SameValueZero(searchElement, elementK) is true, return true.
+        if (sameValueZero(o[k], searchElement)) {
+          return true;
+        }
+        // c. Increase k by 1.
+        k++;
+      }
+
+      // 8. Return false
+      return false;
+    }
+  });
+}
+
+ +

If you need to support truly obsolete JavaScript engines that don't support Object.defineProperty, it's best not to polyfill Array.prototype methods at all, as you can't make them non-enumerable.

+ +

規範

+ + + + + + + + + + + + + + + + + + + +
SpecificationStatusComment
{{SpecName('ES7', '#sec-array.prototype.includes', 'Array.prototype.includes')}}{{Spec2('ES7')}}Initial definition.
{{SpecName('ESDraft', '#sec-array.prototype.includes', 'Array.prototype.includes')}}{{Spec2('ESDraft')}}
+ +

瀏覽器相容性

+ +
+ + +

{{Compat("javascript.builtins.Array.includes")}}

+
+ +

參見

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