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diff --git a/files/zh-cn/web/javascript/reference/global_objects/array/indexof/index.html b/files/zh-cn/web/javascript/reference/global_objects/array/indexof/index.html new file mode 100644 index 0000000000..c470a8b265 --- /dev/null +++ b/files/zh-cn/web/javascript/reference/global_objects/array/indexof/index.html @@ -0,0 +1,197 @@ +--- +title: Array.prototype.indexOf() +slug: Web/JavaScript/Reference/Global_Objects/Array/indexOf +tags: + - JavaScript + - polyfill + - 原型 + - 参考 + - 数组 + - 方法 +translation_of: Web/JavaScript/Reference/Global_Objects/Array/indexOf +--- +<div>{{JSRef}}</div> + +<p><code><strong>indexOf()</strong></code>方法返回在数组中可以找到一个给定元素的第一个索引，如果不存在，则返回-1。</p> + +<div>{{EmbedInteractiveExample("pages/js/array-indexof.html")}}</div> + +<div class="note"> +<p>注意：对于String方法，请参阅 {{jsxref("String.prototype.indexOf()")}}。</p> +</div> + +<h2 id="Syntax" name="Syntax">语法</h2> + +<pre><var>arr</var>.indexOf(<var>searchElement</var>[, <var>fromIndex</var>])</pre> + +<h3 id="参数">参数</h3> + +<dl> + <dt><code>searchElement</code></dt> + <dd>要查找的元素</dd> + <dt><code><var>fromIndex</var></code> {{optional_inline}}</dt> + <dd>开始查找的位置。如果该索引值大于或等于数组长度，意味着不会在数组里查找，返回-1。如果参数中提供的索引值是一个负值，则将其作为数组末尾的一个抵消，即-1表示从最后一个元素开始查找，-2表示从倒数第二个元素开始查找 ，以此类推。 注意：如果参数中提供的索引值是一个负值，并不改变其查找顺序，查找顺序仍然是从前向后查询数组。如果抵消后的索引值仍小于0，则整个数组都将会被查询。其默认值为0.</dd> +</dl> + +<h3 id="返回值">返回值</h3> + +<p>首个被找到的元素在数组中的索引位置; 若没有找到则返回 -1</p> + +<h2 id="描述">描述</h2> + +<p><code>indexOf</code> 使用<a href="/zh-CN/docs/Web/JavaScript/Reference/Operators/Comparison_Operators#Using_the_Equality_Operators">strict equality</a> (无论是 ===, 还是 triple-equals操作符都基于同样的方法)进行判断 <code>searchElement与</code>数组中包含的元素之间的关系。</p> + +<h2 id="示例">示例</h2> + +<h3 id="使用indexOf">使用indexOf</h3> + +<p>以下例子使用<code>indexOf方法确定多个值在数组中的位置。</code></p> + +<pre class="brush: js">var array = [2, 5, 9]; +array.indexOf(2); // 0 +array.indexOf(7); // -1 +array.indexOf(9, 2); // 2 +array.indexOf(2, -1); // -1 +array.indexOf(2, -3); // 0 +</pre> + +<h3 id="找出指定元素出现的所有位置">找出指定元素出现的所有位置</h3> + +<pre class="brush: js">var indices = []; +var array = ['a', 'b', 'a', 'c', 'a', 'd']; +var element = 'a'; +var idx = array.indexOf(element); +while (idx != -1) { + indices.push(idx); + idx = array.indexOf(element, idx + 1); +} +console.log(indices); +// [0, 2, 4] +</pre> + +<h3 id="判断一个元素是否在数组里，不在则更新数组">判断一个元素是否在数组里，不在则更新数组</h3> + +<pre class="brush: js">function updateVegetablesCollection (veggies, veggie) { + if (veggies.indexOf(veggie) === -1) { + veggies.push(veggie); + console.log('New veggies collection is : ' + veggies); + } else if (veggies.indexOf(veggie) > -1) { + console.log(veggie + ' already exists in the veggies collection.'); + } +} + +var veggies = ['potato', 'tomato', 'chillies', 'green-pepper']; + +// New veggies collection is : potato,tomato,chillies,green-papper,spinach +updateVegetablesCollection(veggies, 'spinach'); +// spinach already exists in the veggies collection. +updateVegetablesCollection(veggies, 'spinach'); </pre> + +<h2 id="Polyfill">Polyfill</h2> + +<p><code>indexOf</code> 在ECMA-262 标准 的第5版中被加入，但并非所有的浏览器都支持该方法。你可以在编写scripts时，在其开头使用以下代码，它能够允许你在没有本地支持的情况下使用indexOf方法。该算法符合ECMA-262第5版其中一项规定, 即假定 {{jsxref("Global_Objects/TypeError", "TypeError")}}和 {{jsxref("Math.abs")}} 呈现它们原有的值。</p> + +<pre class="brush: js">// Production steps of ECMA-262, Edition 5, 15.4.4.14 +// Reference: http://es5.github.io/#x15.4.4.14 +if (!Array.prototype.indexOf) { + Array.prototype.indexOf = function(searchElement, fromIndex) { + + var k; + + // 1. Let O be the result of calling ToObject passing + // the this value as the argument. + if (this == null) { + throw new TypeError('"this" is null or not defined'); + } + + var O = Object(this); + + // 2. Let lenValue be the result of calling the Get + // internal method of O with the argument "length". + // 3. Let len be ToUint32(lenValue). + var len = O.length >>> 0; + + // 4. If len is 0, return -1. + if (len === 0) { + return -1; + } + + // 5. If argument fromIndex was passed let n be + // ToInteger(fromIndex); else let n be 0. + var n = +fromIndex || 0; + + if (Math.abs(n) === Infinity) { + n = 0; + } + + // 6. If n >= len, return -1. + if (n >= len) { + return -1; + } + + // 7. If n >= 0, then Let k be n. + // 8. Else, n<0, Let k be len - abs(n). + // If k is less than 0, then let k be 0. + k = Math.max(n >= 0 ? n : len - Math.abs(n), 0); + + // 9. Repeat, while k < len + while (k < len) { + // a. Let Pk be ToString(k). + // This is implicit for LHS operands of the in operator + // b. Let kPresent be the result of calling the + // HasProperty internal method of O with argument Pk. + // This step can be combined with c + // c. If kPresent is true, then + // i. Let elementK be the result of calling the Get + // internal method of O with the argument ToString(k). + // ii. Let same be the result of applying the + // Strict Equality Comparison Algorithm to + // searchElement and elementK. + // iii. If same is true, return k. + if (k in O && O[k] === searchElement) { + return k; + } + k++; + } + return -1; + }; +} +</pre> + +<h2 id="规范">规范</h2> + +<table class="standard-table"> + <tbody> + <tr> + <th scope="col">Specification</th> + <th scope="col">Status</th> + <th scope="col">Comment</th> + </tr> + <tr> + <td>{{SpecName('ES5.1', '#sec-15.4.4.14', 'Array.prototype.indexOf')}}</td> + <td>{{Spec2('ES5.1')}}</td> + <td>Initial definition.<br> + Implemented in JavaScript 1.6</td> + </tr> + <tr> + <td>{{SpecName('ES6', '#sec-array.prototype.indexof', 'Array.prototype.indexOf')}}</td> + <td>{{Spec2('ES6')}}</td> + <td></td> + </tr> + </tbody> +</table> + +<h2 id="浏览器兼容性">浏览器兼容性</h2> + +<div> + + +<p>{{Compat("javascript.builtins.Array.indexOf")}}</p> +</div> + +<h2 id="See_also" name="See_also">相关链接</h2> + +<ul> + <li>{{jsxref("Array.prototype.lastIndexOf()")}}</li> + <li>{{jsxref("TypedArray.prototype.indexOf()")}}</li> +</ul> |