jQuery的serialize模块中有个r20正则
var r20 = /%20/g,
jQuery.param方法中会将所有的"%20"转成"+"，即提交数据前，数据中如果包含空格，那经过encodeURIComponent后，空格会转成"%20"
encodeURIComponent(' ') === '%20'; // true
最后需要将"%20"转换成"="再Post提交。这样后台程序接受到的才是真正的空格。
关于 encodeURIComponent，见MDC描述
encodeURIComponent escapes all characters except the following: alphabetic, decimal digits, - _ . ! ~ * ' ( )
To avoid unexpected requests to the server, you should call encodeURIComponent on any user-entered parameters that will be passed as part of a URI. For example, a user could type "Thyme &time=again" for a variable comment. Not using encodeURIComponent on this variable will give comment=Thyme%20&time=again. Note that the ampersand and the equal sign mark a new key and value pair. So instead of having a POST comment key equal to "Thyme &time=again", you have two POST keys, one equal to "Thyme " and another (time) equal to again.
For application/x-www-form-urlencoded (POST), per http://www.w3.org/TR/html401/interac...m-content-type, spaces are to be replaced by '+', so one may wish to follow a encodeURIComponent replacement with an additional replacement of "%20" with "+".
相关：
https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/encodeURIComponent
http://www.w3.org/TR/html401/interact/forms.html#form-content-type
