使用jQuery的将桌面应用程序引入浏览器

<script type="text/javascript" src="jquery.js"></script>

// Incorrect
<script language=JavaScript>
 $("div").addClass("a");
</script>

// Correct
$(document).ready(function(){
 $("div").addClass("a");
 });

// - or -

$(document).ready(function(){
 myAddClass();
 });

function myAddClass()
{
 $("div").addClass("a");
}

String man = new String("manipulated").toUpperCase().substring(0,5).toLowerCase();

$("div").addClass("a").show().text("manipulated");

j$ = jQuery.noConflict();
j$("div").addClass("a");

选择


jQuery 的根本在于它在页面上选择和操作某些元素的能力。从某种意义上说，需要围绕这些对象才能构建出有效的 jQuery 库。因此，面对一个普通 HTML 页面上提供的大量选项，您需要一种方法来快速高效地选择您需要在页面上使用的元素，只选择需要的元素（不多也不少）。jQuery 如我们所愿地提供了一些强大的选择方法，帮助我们在页面上寻找和选择对象。jQuery 创建了它自己的选择语法，并且这种语法很容易掌握。


（以下大部分示例所使用的函数将留在下一篇中讨论，不过它们的功能应该是很直观明了的）。


根本上来讲，jQuery 中的选择过程就是一个巨大的过滤过程，页面上的每个元素都经过这个过滤器，它将返回一个匹配的对象，或一个可以遍历的匹配对象的数组。


排在前面的 3 个示例是最常用的。它们通过 HTML 标记、ID 或 CLASS 查找对象。


HTML


要获取一个页面中所有匹配的 HTML 元素的数组，您仅需将 HTML 标记（不带括号）传递到 jQuery 搜索字段。这是查找对象的 “快速但是粗糙” 的方法。如果要将属性附加到通用的 HTML 元素，这种方法是很有用的。


清单 5. HTML 选择

 
// This will show every <div> tag in the page. Note that it will show 
// every <div>, not the first matching, or the last matching. 
// Traversing Arrays is discussed later in the article.
$("div").show();

// This will give a red background to every <p> tag in the page.
$("p").css("background", "#ff0000");

// This will set the innerHTML of a span element with the id of "sampleText" to "Hi". 
// Note the initial "#" in the command. This is the syntax used by jQuery to search 
// for IDs, and must be included. If it is excluded, jQuery will search for the HTML
// tag instead, and with no <sampleText> tags on a page, will ultimately do
// nothing, leading to frustrating and hard-to-find bugs (not that that has ever 
// happened to me of course).

$("#sampleText").html("Hi");

// This will create a red background on every element on the page with a CLASS of 
// "redBack". Notice that it doesn't matter which HTML element this "redBack" 
// CLASS tag is attached to. Also notice the period in the front of the query
// term -- this is the jQuery syntax for finding the CLASS names.

$(".redBack").css("background", "#ff0000");

<p class="redBack">This is a paragraph</p>
<div class="redBack">This is a big div</div>
<table class="redBack"><tr><td>Sample table</td></tr></table>

// This will hide every <p>, <span>, or <div>.
$("p, span, div").hide();

// This will hide every <p> tag on a page
$("p").hide();

// This will hide the first element on a page, no matter its HTML tag
$(":first").hide();

// Notice how these can be used in combination to provide more fine tuning of 
// search criteria. This will hide only the first <p> tag on a given page.
$("p:first").hide();

// Will loop through each <p> tag on the page. Notice the use of the
// inline function here -- this is analogous with the anonymous classes in Java.
// You can either call a separate function, or write an inline function like this.

var increment = 1;
$("p").each(function(){

 // now add a paragraph count in front of each of them. Notice how we use the
 // $(this) variable to reference each of the paragraph elements individually.

 $(this).text(increment + ". " + $(this).text());
 increment++;
});

// the eq() function lets you reference an element in the array directly. 
// In this case, it will get the 3rd paragraph (0 referenced of course) and hide it
$("p").eq(2).hide();

// The slice() function lets you input a start and an end index in the array, to 
// create a subset of the array. This will hide the 3rd through 5th paragraphs on the
// page
$("p").slice(2,5).hide();

<input type=text class=validate><span></span>

function validateForm()
{
 $(".validate:text").each(function(){
 if ($(this).val()=="")
 // We'll loop through each textfield on the page with a class of "validate"
 // and if they are blank, we will put text in the <span> immediately afterwards
 // with the error message.

  $(this).next().html("This field cannot be blank");
});
}

<!-- The first step is creating the Select All checkbox itself.
we give it a unique ID on the page -->

<input type=checkbox id=selectall>

<!-- The next step is giving each of the rows their own checkbox.
we put each row's checkbox into the 'selectable' class, since there can be many rows,
and we want each of the rows' checkboxes to have the same behavior. -->

<input type=checkbox class=selectable>

<!-- The final step is bringing it all together with some jQuery code. -->

// remember that all jQuery setup code must be in this document.ready() function, 
// or contained within its own function in order to function correctly.

$(document).ready(function(){
 // We use the jQuery selection syntax to find the selectall checkbox on the page
 // (note the '#' which signifies ID), and we tell jQuery to call the selectAll()
 // function every time someone clicks on the checkbox (we'll get to Events in a
 // future article).

 $("#selectall").click(selectAll);
});

// This function will get called every time someone clicks on the selectall checkbox
function selectAll()
{
 // this line determines if the selectall checkbox is checked or not. The attr()
 // function, discussed in a future article, simply returns an attribute on the
 // given object. In this case, it returns a boolean if true, or an undefined if
 // it's not checked.

 var checked = $("#selectall").attr("checked");

 // Now we use the jQuery selection syntax to find all the checkboxes on the page
 // with the selectable class added to them (each row's checkbox). We get an array
 // of results back from this selection, and we can iterate through them using the
 // each() function, letting us work with each result one at a time. Inside the
 // each() function, we can use the $(this) variable to reference each individual
 // result. Thus, inside each loop, it finds the value of each checkbox and matches
 // it to the selectall checkbox.

 $(".selectable").each(function(){
  var subChecked = $(this).attr("checked");
  if (subChecked != checked)
   $(this).click();
 });
}