jQuery学习（2）ajax()使用
在上一篇分享JavaScript之使用AJAX（适合初学者）中，我们学习了如何在JavaScript中使用AJAX.由于jQuery出色的性能和简洁的写法，且它也支持AJAX的使用，所以，本次分享将会展示如何在jQuery中使用ajax()函数。
关于jQuery的ajax()函数的教程，可以参考：http://www.w3school.com.cn/jquery/jquery_ref_ajax.asp ，当然，我们也可以jQuery.ajax()的官方文档：http://api.jquery.com/jquery.ajax/，该官方文档不仅详细地介绍了该函数各个参数以及它们的含义，并且还给出了许多例子，值得一看。
关于Web服务器以及文件的配置，我们还是跟前一篇保持一致。接下来，我们将看一个具体的例子。
首先，我们的开始页面（city_intro.html）如下：
该页面的完整代码如下：
<!DOCTYPE html>
<html>
<head>
<script src="https://cdn.bootcss.com/jquery/3.2.1/jquery.js"></script>
<script>
$(document).ready(function(){
$("#btn1").click(function(){
var city = $('#city').val();
htmlobj=$.ajax({
method: "POST",
url: "demo.php",
data: {query:city},
async:false,
});
$("#demo").html(htmlobj.responseText);
});
$("#btn2").click(function(){ location.reload(); });
});
</script>
</head>
<body>
<h3>City Introduction</h3>
<form>
City:
<select id='city'>
<option>Shanghai</option>
<option>Tokyo</option>
<option>New York</option>
</select>
</form>
<br>
<button id="btn1">Submit</button>
<button id="btn2">REFRESH</button>
<p id='demo'></p>
</body>
</html>上述代码中，我们调用了ajax(）函数，里面的参数含义如下：
- method: 请求方式，’GET’或者’POST’;
- url: 服务器上的文件网址；
- data: 发送到服务器的数据;
- async: 是否异步.
demo.php的完整代码如下：
<?php
$citys = array();
$citys["Shanghai"] = "Shanghai is one of the four direct-controlled municipalities of China and the most populous
city proper in the world, with a population of more than 24 million as of 2014.It is a global
financial center and transport hub, with the world's busiest container port. Located in the
Yangtze River Delta, it sits on the south edge of the estuary of the Yangtze in the middle
portion of the East China coast. The municipality borders the provinces of Jiangsu and Zhejiang
to the north, south and west, and is bounded to the east by the East China Sea.";
$citys["Tokyo"] = "Tokyo is the capital city of Japan and one of its 47 prefectures. The Greater Tokyo Area is the most
populous metropolitan area in the world. It is the seat of the Emperor of Japan and the Japanese
government. Tokyo is in the Kantō region on the southeastern side of the main island Honshu and includes
the Izu Islands and Ogasawara Islands. Formerly known as Edo, it has been the de facto seat of government
since 1603 when Shogun Tokugawa Ieyasu made the city his headquarters. It officially became the capital
after Emperor Meiji moved his seat to the city from the old capital of Kyoto in 1868; at that time Edo was
renamed Tokyo. Tokyo Metropolis was formed in 1943 from the merger of the former Tokyo Prefecture and
the city of Tokyo.";
$citys["New York"] = "The City of New York, often called New York City or simply New York, is the most populous city in the
United States. With an estimated 2016 population of 8,537,673 distributed over a land area of about
302.6 square miles (784 km2), New York City is also the most densely populated major city in the
United States. Located at the southern tip of the state of New York, the city is the center of the
New York metropolitan area, one of the most populous urban agglomerations in the world with an estimated
23.7 million residents as of 2016. A global power city, New York City has been described as the cultural,
financial, and media capital of the world, and exerts a significant impact upon commerce, entertainment,
research, technology, education, politics, and sports. The city's fast pace defines the term New York minute.
Home to the headquarters of the United Nations, New York is an important center for international diplomacy.";
$query = $_POST["query"];
echo $citys[$query];
?> 这样我们可以在页面上进行操作了，点击‘Shanghai’,显示的页面如下：
点击‘New York’,显示的页面如下：
本次分享到此结束，欢迎大家交流~~
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