在JavaScript中使用json.js：Ajax项目之POST请求（异步）

经常在百度搜索框输入一部分关键词后，弹出候选关键热词。现在我们就用Ajax技术来实现这一功能。

一、下载json.js文件

百度搜一下，最好到json官网下载，安全起见。

并与新建的两个文件部署如图

json.js也可直接复制此处的代码获取。

 /*
     json.js
     2008-03-14

     Public Domain

     No warranty expressed or implied. Use at your own risk.

     This file has been superceded by http://www.JSON.org/json2.js

     See http://www.JSON.org/js.html

     This file adds these methods to JavaScript:

         array.toJSONString(whitelist)
         boolean.toJSONString()
         date.toJSONString()
         number.toJSONString()
         object.toJSONString(whitelist)
         string.toJSONString()
             These methods produce a JSON text from a JavaScript value.
             It must not contain any cyclical references. Illegal values
             will be excluded.

             The default conversion for dates is to an ISO string. You can
             add a toJSONString method to any date object to get a different
             representation.

             The object and array methods can take an optional whitelist
             argument. A whitelist is an array of strings. If it is provided,
             keys in objects not found in the whitelist are excluded.

         string.parseJSON(filter)
             This method parses a JSON text to produce an object or
             array. It can throw a SyntaxError exception.

             The optional filter parameter is a function which can filter and
             transform the results. It receives each of the keys and values, and
             its return value is used instead of the original value. If it
             returns what it received, then structure is not modified. If it
             returns undefined then the member is deleted.

             Example:

             // Parse the text. If a key contains the string 'date' then
             // convert the value to a date.

             myData = text.parseJSON(function (key, value) {
                 return key.indexOf('date') >= 0 ? new Date(value) : value;
             });

     It is expected that these methods will formally become part of the
     JavaScript Programming Language in the Fourth Edition of the
     ECMAScript standard in 2008.

     This file will break programs with improper for..in loops. See
     http://yuiblog.com/blog/2006/09/26/for-in-intrigue/

     This is a reference implementation. You are free to copy, modify, or
     redistribute.

     Use your own copy. It is extremely unwise to load untrusted third party
     code into your pages.
 */

 /*jslint evil: true */

 /*members "\b", "\t", "\n", "\f", "\r", "\"", "\\", apply, charCodeAt,
     floor, getUTCDate, getUTCFullYear, getUTCHours, getUTCMinutes,
     getUTCMonth, getUTCSeconds, hasOwnProperty, join, length, parseJSON,
     prototype, push, replace, test, toJSONString, toString
 */

 // Augment the basic prototypes if they have not already been augmented.

 if (!Object.prototype.toJSONString) {

     Array.prototype.toJSONString = function (w) {
         var a = [],     // The array holding the partial texts.
             i,          // Loop counter.
             l = this.length,
             v;          // The value to be stringified.

 // For each value in this array...

         for (i = 0; i < l; i += 1) {
             v = this[i];
             switch (typeof v) {
             case 'object':

 // Serialize a JavaScript object value. Treat objects thats lack the
 // toJSONString method as null. Due to a specification error in ECMAScript,
 // typeof null is 'object', so watch out for that case.

                 if (v && typeof v.toJSONString === 'function') {
                     a.push(v.toJSONString(w));
                 } else {
                     a.push('null');
                 }
                 break;

             case 'string':
             case 'number':
             case 'boolean':
                 a.push(v.toJSONString());
                 break;
             default:
                 a.push('null');
             }
         }

 // Join all of the member texts together and wrap them in brackets.

         return '[' + a.join(',') + ']';
     };

     Boolean.prototype.toJSONString = function () {
         return String(this);
     };

     Date.prototype.toJSONString = function () {

 // Eventually, this method will be based on the date.toISOString method.

         function f(n) {

 // Format integers to have at least two digits.

             return n < 10 ? '0' + n : n;
         }

         return '"' + this.getUTCFullYear()   + '-' +
                    f(this.getUTCMonth() + 1) + '-' +
                    f(this.getUTCDate())      + 'T' +
                    f(this.getUTCHours())     + ':' +
                    f(this.getUTCMinutes())   + ':' +
                    f(this.getUTCSeconds())   + 'Z"';
     };

     Number.prototype.toJSONString = function () {

 // JSON numbers must be finite. Encode non-finite numbers as null.

         return isFinite(this) ? String(this) : 'null';
     };

     Object.prototype.toJSONString = function (w) {
         var a = [],     // The array holding the partial texts.
             k,          // The current key.
             i,          // The loop counter.
             v;          // The current value.

 // If a whitelist (array of keys) is provided, use it assemble the components
 // of the object.

         if (w) {
             for (i = 0; i < w.length; i += 1) {
                 k = w[i];
                 if (typeof k === 'string') {
                     v = this[k];
                     switch (typeof v) {
                     case 'object':

 // Serialize a JavaScript object value. Ignore objects that lack the
 // toJSONString method. Due to a specification error in ECMAScript,
 // typeof null is 'object', so watch out for that case.

                         if (v) {
                             if (typeof v.toJSONString === 'function') {
                                 a.push(k.toJSONString() + ':' +
                                        v.toJSONString(w));
                             }
                         } else {
                             a.push(k.toJSONString() + ':null');
                         }
                         break;

                     case 'string':
                     case 'number':
                     case 'boolean':
                         a.push(k.toJSONString() + ':' + v.toJSONString());

 // Values without a JSON representation are ignored.

                     }
                 }
             }
         } else {

 // Iterate through all of the keys in the object, ignoring the proto chain
 // and keys that are not strings.

             for (k in this) {
                 if (typeof k === 'string' &&
                         Object.prototype.hasOwnProperty.apply(this, [k])) {
                     v = this[k];
                     switch (typeof v) {
                     case 'object':

 // Serialize a JavaScript object value. Ignore objects that lack the
 // toJSONString method. Due to a specification error in ECMAScript,
 // typeof null is 'object', so watch out for that case.

                         if (v) {
                             if (typeof v.toJSONString === 'function') {
                                 a.push(k.toJSONString() + ':' +
                                        v.toJSONString());
                             }
                         } else {
                             a.push(k.toJSONString() + ':null');
                         }
                         break;

                     case 'string':
                     case 'number':
                     case 'boolean':
                         a.push(k.toJSONString() + ':' + v.toJSONString());

 // Values without a JSON representation are ignored.

                     }
                 }
             }
         }

 // Join all of the member texts together and wrap them in braces.

         return '{' + a.join(',') + '}';
     };

     (function (s) {

 // Augment String.prototype. We do this in an immediate anonymous function to
 // avoid defining global variables.

 // m is a table of character substitutions.

         var m = {
             '\b': '\\b',
             '\t': '\\t',
             '\n': '\\n',
             '\f': '\\f',
             '\r': '\\r',
             '"' : '\\"',
             '\\': '\\\\'
         };

         s.parseJSON = function (filter) {
             var j;

             function walk(k, v) {
                 var i, n;
                 if (v && typeof v === 'object') {
                     for (i in v) {
                         if (Object.prototype.hasOwnProperty.apply(v, [i])) {
                             n = walk(i, v[i]);
                             if (n !== undefined) {
                                 v[i] = n;
                             } else {
                                 delete v[i];
                             }
                         }
                     }
                 }
                 return filter(k, v);
             }

 // Parsing happens in three stages. In the first stage, we run the text against
 // a regular expression which looks for non-JSON characters. We are especially
 // concerned with '()' and 'new' because they can cause invocation, and '='
 // because it can cause mutation. But just to be safe, we will reject all
 // unexpected characters.

 // We split the first stage into 4 regexp operations in order to work around
 // crippling inefficiencies in IE's and Safari's regexp engines. First we
 // replace all backslash pairs with '@' (a non-JSON character). Second, we
 // replace all simple value tokens with ']' characters. Third, we delete all
 // open brackets that follow a colon or comma or that begin the text. Finally,
 // we look to see that the remaining characters are only whitespace or ']' or
 // ',' or ':' or '{' or '}'. If that is so, then the text is safe for eval.

             if (/^[\],:{}\s]*$/.test(this.replace(/\\["\\\/bfnrtu]/g, '@').
                     replace(/"[^"\\\n\r]*"|true|false|null|-?\d+(?:\.\d*)?(?:[eE][+\-]?\d+)?/g, ']').
                     replace(/(?:^|:|,)(?:\s*\[)+/g, ''))) {

 // In the second stage we use the eval function to compile the text into a
 // JavaScript structure. The '{' operator is subject to a syntactic ambiguity
 // in JavaScript: it can begin a block or an object literal. We wrap the text
 // in parens to eliminate the ambiguity.

                 j = eval('(' + this + ')');

 // In the optional third stage, we recursively walk the new structure, passing
 // each name/value pair to a filter function for possible transformation.

                 return typeof filter === 'function' ? walk('', j) : j;
             }

 // If the text is not JSON parseable, then a SyntaxError is thrown.

             throw new SyntaxError('parseJSON');
         };

         s.toJSONString = function () {

 // If the string contains no control characters, no quote characters, and no
 // backslash characters, then we can simply slap some quotes around it.
 // Otherwise we must also replace the offending characters with safe
 // sequences.

             if (/["\\\x00-\x1f]/.test(this)) {
                 return '"' + this.replace(/[\x00-\x1f\\"]/g, function (a) {
                     var c = m[a];
                     if (c) {
                         return c;
                     }
                     c = a.charCodeAt();
                     return '\\u00' + Math.floor(c / 16).toString(16) +
                                                (c % 16).toString(16);
                 }) + '"';
             }
             return '"' + this + '"';
         };
     })(String.prototype);
 }

json.js

二、客户端（suggest.html）

创建一个基于POST请求类型的Ajax项目页面suggest.html

 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
 <html xmlns="http://www.w3.org/1999/xhtml">
     <head>
         <script type="text/javascript" src="json.js"></script>
         <script type="text/javascript">
             //为XHR对象创建全局变量
             var xhr;

             function getXHR(){//获取跨浏览器的XmlHttpRequest对象
                 var req;
                 if (window.XMLHttpRequest) {
                     req= new XMLHttpRequest();
                 }else if(window.ActiveXObject){
                     req= new ActiveXObject("Microsoft.XMLHTTP");
                 }
                 return req;
             }

             function suggest(){
                 //如果还有未处理完的XHR请求正在进行，就中断它
                 if (xhr && xhr.readyState !=0) {
                     xhr.abort();
                 }

                 xhr=getXHR();

                 //创建异步POST请求(根据需求，修改这行代码)
                 xhr.open("POST","suggest.php",true);

                 //读取搜索框中的值
                 searchValue=document.getElementById("search").value;

                 //以URL编码格式编码数据
                 data="search="+ encodeURIComponent(searchValue);

                 //定义接收状态变更通知的函数
                 xhr.onreadystatechange=readyStateChange;

                 //设置请求头信息，以便让PHP知道这是一个表单提交
                 xhr.setRequestHeader("Content-type","application/x-www-form-urlencoded");

                 //将数据传送到服务器上
                 xhr.send(data);
             }

             function readyStateChange(){
                 //状态4表示数据已经准备好了
                 if (xhr.readyState==4) {

                     //检查服务器是否发送了数据，并且请求是200OK
                     if (xhr.responseText && xhr.status==200) {
                         json=xhr.responseText;

                         //解析服务器的响应内容，创建一个JS数组
                         try{
                             suggestionArr=json.parseJSON();
                         }catch(e){
                             //解析数据遇到问题
                             alert("解析数据遇到问题");
                         }

                         //创建一些HTML文本
                         tmpHtml="";
                         for (i=0;i<suggestionArr.length;i++) {
                             tmpHtml+= suggestionArr[i]+"<br />";
                         }

                         div=document.getElementById("suggestions");
                         div.innerHTML=tmpHtml;
                     }
                 }
             }

         </script>
     </head>
     <body>
         <input id="search" type="text" onkeyup="suggest()"/>
         <div id="suggestions"></div>
     </body>
 </html>

suggest.html

三、服务端（suggest.php）

创建一个基于POST请求类型的Ajax项目程序suggest.php

 <?php
     $arr=array(
         'zhangsan','lisi',
         'wangwu','zhaoliu',
         'andy','admin','安迪'
     );

     $search=strtolower($_POST['search']);

     $hits=array();
     if (!empty($search)) {
         foreach ($arr as $name) {
             if (strpos(strtolower($name),$search)===0) {
                 $hits[]=$name;
             }
         }
     }

     echo json_encode($hits);
 ?>

suggest.php

输出结果：