Jquery是继prototype之后又一个优秀的Javascrīpt框架。它是轻量级的js库(压缩后只有21k) ，它兼容CSS3，还兼容各种浏览器 （IE 6.0+, FF 1.5+, Safari 2.0+, Opera 9.0+）。jQuery使用户能更方便地处理HTML documents、events、实现动画效果，并且方便地为网站提供AJAX交互。jQuery还有一个比较大的优势是，它的文档说明很全，而且各种应用也说得很详细，同时还有许多成熟的插件可供选择。jQuery能够使用户的html页保持代码和html内容分离，也就是说，不用再在html里面插入一堆js来调用命令了，只需定义id即可。
We’re nearing the first update to jQuery 1.5 – and we’re pleased to announce the release of the first release candidate! Barring any major bugs this should be the code that we end up shipping for jQuery 1.5.1 (which will be happening on February 24th).
You can get the code from the jQuery CDN:
http://code.jquery.com/jquery-1.5.1rc1.js
You can help us by dropping that code into your existing application and letting us know that if anything no longer works. Please file a bug and be sure to mention that you’re testing against jQuery 1.5.1 RC 1.
We want to encourage everyone from the community to try and get involved in contributing back to jQuery core. We’ve set up a full page of information dedicated towards becoming more involved with the team. The team is here and ready to help you help us!
更新日志：
#2551 Make sure .val() works after form.reset() in IE
#4537 Make sure .clone(true) correctly clones namespaced events
#4966 Don’t add “px” to unit-less properties when animating them
#6774 Make sure we only access parentNode if it’s available. Fixes an issue where after an option tag has been detached, an elem.parentNode error would be thrown.
#7531 Fix again for IE9RC. Enhances ajaxSetup so that it can take an optional target option, in which case target will be updated instead of ajaxSettings. That way, fields that shouldn’t be deep extended can be listed and dealt with in one place. jQuery.ajax now makes use of ajaxSetup with target to create its internal settings object
#7568 Follow-up fix for #5862. Objects with a length property weren’t serialized properly by jQuery.param
#7653 Changes regexp to detect local protocol so that it will accept any protocol finishing by -extension
#7668 Sizzle and jQuery QUnit tests are out of sync
#7912 This change makes .cur() more .cssHooks friendly. .cur() now returns the unmodified value by .css() if it isn’t a number, number-alike or a value that needs a fallback to 0.
#7922 Fixed an issue where live(‘click’) doesn’t fire when live(‘submit’) is bound first in IE
#7945 Make jQuery.param() serialize plain objects with a property named jquery correctly
#8033 jQuery 1.4.4+ fails to load on pages with old Prototype (<= 1.5) or Current Prototype + Scriptaculous in IE
#8039 Selectors with HTML5 input types not work in IE6/7
#8052 Update jQuery.support.noCloneEvent test to function properly in IE9
#8095 Properly handles the case where browser cache needs to be bypassed while server-side logic still delivers proper 304 responses. Unit test added
#8098 Use the fast document.head when available
#8099 Always restore to correct display value based on element’s expected default display
#8107 Fix argument handling for $.ajax for multiple method signatues and add test case
#8108Temporary fix for jQuery metadata being exposed on plain JS objects when serializing with JSON.stringify to avoid compatibility-breaking changes. A proper fix for this will be landed in 1.6
#8115 Renames all references to jXHR with jqXHR in the code (like was done in the doc)
#8123 The default for .clone() is to not clone any events
#8125 Status is set to 200 for requests with status 0 when location.protocol if “file:”. Added test/localfile.html to control it works
#8129 Fix cloning multiple selected options in IE8
#8135 Makes sure any exception thrown by Firefox when trying to access an XMLHttpRequest property when a network error occured is caught and notified as an error. Added test/networkerror.html to test the behavior
#8138 Access to document.location is made only once at load time and if it fails (throwing an exception in IE when document.domain is already set), we use the href of an A element instead
#8145 Added readyWait tests
#8146 introducing the xhrFields option with is a map of fieldName/fieldValue to set on the native xhr. Can be used to set withCredentials to true for cross-domain requests if needed
#8152 applying the same special cases for protocol “chrome-extension:” as were for “file:” (needs tests). Re-organizes and fixes the handling of special cases for HTTP status code in the xhr transport
#8177 XHR transport now considers 304 Not Modified responses as 200 OK if no conditional request header was provided (as per the XMLHttpRequest specification)
#8193 Fixes abort in prefilter. No global event will be fired in that case even if the global option is set to true. Unit test added
#8198 Remove unnecessary “script.type = text/javascript;”
#8200 Unexpose $.support._scriptEval as it’s not needed. Use a private var instead
#8209 Make sure that mousing over Chrome “internal div” doesn’t trigger a mouseleave
#8219 Introduces the mimeType option to override content-type header in conversion (and in native xhr when possible). Adds companion overrideMimeType method on jqXHR object (it simply sets the option)
#8220 Remove backslashes from tag name filter
#8245 Ajax now ensures header names are capitalized so that non-compliant xhr implementations don’t override them
#8250 ajax does not work in opera 10 widgets
#8277 Sets data to undefined rather than null when it is not provided in ajax helpers so that it won’t revent data set in ajaxSettings from being used.
#8297 Make sure response headers with empty values are handled properly and do not prevent proper parsing of the entire response headers string.