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$.each 和$(selector).each()的区别

2024-07-18 18:26:10   219人阅读

译自官方手册:jQuery.each()

对数组或对对象内容进行循环处理

jQuery.each( collection, callback(indexInArray, valueOfElement) )

collection   遍历的对象或数组

callback(indexInArray, valueOfElement) 在每一个对象上调用的函数

说明

一个通用的遍历函数 , 可以用来遍历对象和数组. 数组和含有一个length属性的伪数组对象 (伪数组对象如function的arguments对象)以数字索引进行遍历,从0到length-1, 其它的对象通过的属性进行遍历.

$.each()与$(selector).each()不同, 后者专用于jquery对象的遍历, 前者可用于遍历任何的集合(无论是数组或对象),如果是数组,回调函数每次传入数组的索引和对应的值(值亦可以通过this 关键字获取,但javascript总会包装this 值作为一个对象—尽管是一个字符串或是一个数字),方法会返回被遍历对象的第一参数

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//例子:———传入数组

<!DOCTYPE html> < html> < head> < script src=http://www.mamicode.com/”http://code.jquery.com/jquery-latest.js”></script> < /head> < body> < script>

$.each([52, 97], function(index, value) { alert(index + ‘: ‘ + value); });

</script> < /body> < /html>

//输出

0: 52 1: 97

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//例子:———如果一个映射作为集合使用,回调函数每次传入一个键-值对

<!DOCTYPE html> < html> < head> < script src=http://www.mamicode.com/”http://code.jquery.com/jquery-latest.js”></script> < /head> < body> < script>

var map = { ‘flammable’: ‘inflammable’, ‘duh’: ‘no duh’ }; $.each(map, function(key, value) { alert(key + ‘: ‘ + value); });

</script> < /body> < /html>

//输出

flammable: inflammable duh: no duh

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//例子:———回调函数中 return false时可以退出$.each(), 如果返回一个非false 即会像在for循环中使用continue 一样, 会立即进入下一个遍历

<!DOCTYPE html>

<html>

<head>

  <style>

  div { color:blue; }

  div#five { color:red; }

  </style>

  <script src=http://www.mamicode.com/”http://code.jquery.com/jquery-latest.js”></script>

</head>

<body>

  <div id=”one”></div>

  <div id=”two”></div>

  <div id=”three”></div>

  <div id=”four”></div>

  <div id=”five”></div>

<script>

    var arr = [ "one", "two", "three", "four", "five" ];//数组

    var obj = { one:1, two:2, three:3, four:4, five:5 }; // 对象

    jQuery.each(arr, function() {  // this 指定值

      $(“#” + this).text(“Mine is ” + this + “.”);  // this指向为数组的值, 如one, two

       return (this != “three”); // 如果this = three 则退出遍历

   });

    jQuery.each(obj, function(i, val) {  // i 指向键, val指定值

      $(“#” + i).append(document.createTextNode(” – ” + val));

    });

</script>

</body>

</html>

// 输出

Mine is one. – 1
Mine is two. – 2
Mine is three. – 3
- 4
- 5
 
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//例子:———遍历数组的项, 传入index和value

<!DOCTYPE html> < html> < head> < script src=http://www.mamicode.com/”http://code.jquery.com/jquery-latest.js”></script> < /head> < body> < script>

$.each( [‘a‘,‘b‘,‘c‘], function(i, l){ alert( “Index #” + i + “: ” + l ); });

</script> < /body> < /html>

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//例子:———遍历对象的属性,传入 key和value

<!DOCTYPE html> < html> < head> < script src=http://www.mamicode.com/”http://code.jquery.com/jquery-latest.js”></script> < /head> < body> < script>

$.each( { name: “John”, lang: “JS” }, function(k, v){ alert( “Key: ” + k + “, Value: ” + v ); });

</script> < /body> < /html>

正自评论的例子:

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1. 如果不想输出第一项 (使用retrun true)进入 下一遍历

<!DOCTYPE html> < html> < head> < script src=http://www.mamicode.com/”http://code.jquery.com/jquery-latest.js”></script> < /head> < body> < script>

var myArray=["skipThis", "dothis", "andThis"]; $.each(myArray, function(index, value) { if (index == 0) { return true; // equivalent to ‘continue’ with a normal for loop } // else do stuff… alert (index + “: “+ value); });

</script> < /body> < /html>


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