jQuery实现jsonp源码分析,京东2015面试
// Bind script tag hack transport
jQuery.ajaxTransport( "script", function(s) {
// This transport only deals with cross domain requests
if ( s.crossDomain ) {
var script,
head = document.head || jQuery("head")[0] || document.documentElement;
return {
send: function( _, callback ) {
script = document.createElement("script");
script.async = true;
if ( s.scriptCharset ) {
script.charset = s.scriptCharset;
}
script.src = s.url;
// Attach handlers for all browsers
script.onload = script.onreadystatechange = function( _, isAbort ) {
if ( isAbort || !script.readyState || /loaded|complete/.test( script.readyState ) ) {
// Handle memory leak in IE
script.onload = script.onreadystatechange = null;
// Remove the script
if ( script.parentNode ) {
script.parentNode.removeChild( script );
}
// Dereference the script
script = null;
// Callback if not abort
if ( !isAbort ) {
callback( 200, "success" );
}
}
};
// Circumvent IE6 bugs with base elements (#2709 and #4378) by prepending
// Use native DOM manipulation to avoid our domManip AJAX trickery
head.insertBefore( script, head.firstChild );
},
abort: function() {
if ( script ) {
script.onload( undefined, true );
}
}
};
}
});
var oldCallbacks = [],
rjsonp = /(=)\?(?=&|$)|\?\?/;
// Default jsonp settings
jQuery.ajaxSetup({
jsonp: "callback",
jsonpCallback: function() {
var callback = oldCallbacks.pop() || ( jQuery.expando + "_" + ( ajax_nonce++ ) );
this[ callback ] = true;
return callback;
}
});
jsonp的实现与原理:
$.ajax({
url: 'http://192.168.1.114/yii/demos/test.php', //不同的域
type: 'GET', // jsonp模式只有GET是合法的
data: {
'action': 'aaron'
}, // 预传参的数组
dataType: 'jsonp', // 数据类型
jsonp: 'backfunc', // 指定回调函数名,与服务器端接收的一致,并回传回来
})
其实jquery内部会转化成
http://192.168.1.114/yii/demos/test.php?backfunc=jQuery2030038573939353227615_1402643146875&action=aaron;
然后动态加载
<script type="text/javascript" src="http://192.168.1.114/yii/demos/test.php?backfunc=jQuery2030038573939353227615_1402643146875&action=aaron"></script>
问题:backfunc=jQuery2030038573939353227615_1402643146875是怎么产生的?
jsonpCallback: function() {
var callback = oldCallbacks.pop() || ( jQuery.expando + "_" + ( ajax_nonce++ ) );
}
expando: "jQuery" + ( core_version + Math.random() ).replace( /\D/g, "" );
ajax_nonce = jQuery.now();
//如果没有设置jsonpCallback的话就把callback的名字(jsonpCallback)随机设置为jQuery+版本号+随机数+_$.now()现在的时间
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