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Best way to use Google's hosted jQuery, but fall back to my hosted library on Google fail

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太阳男子
太阳男子 2020-11-21 07:19

What would be a good way to attempt to load the hosted jQuery at Google (or other Google hosted libs), but load my copy of jQuery if the Google attempt fails?

I\'m n

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23条回答
  • 你的背包
    2020-11-21 07:57
    • Step 1: Did jQuery fail to load? (check jQuery variable)

    How to check a not-defined variable in JavaScript

    • Step 2: Dynamically import (the backup) javascript file

    How do I include a JavaScript file in another JavaScript file?

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  • 爱一瞬间的悲伤
    2020-11-21 07:58

    Because of the Google's banning problem I prefer to use Microsoft's cdn http://www.asp.net/ajaxlibrary/cdn.ashx

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  • 时光取名叫无心
    2020-11-21 07:58

    UPDATE:
    This answer turned out to be wrong. Please see the comments for the real explanation.

    Most of you question has been answered, but as for the final part:

    What would be the danger of both copies coming through?

    None really. You'd waste bandwidth, might add some milliseconds downloading a second useless copy, but there's not actual harm if they both come through. You should, of course, avoid this using the techniques mentioned above.

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  • 逝去的感伤
    2020-11-21 07:58

    Yet another fallback that replaces ajax.googleapis.com with cdnjs.cloudflare.com:

    (function (doc, $)
{
    'use strict';

    if (typeof $ === 'undefined')
    {
        var script = doc.querySelector('script[src*="jquery.min.js"]'),
            src = script.src.replace('ajax.googleapis.com', 'cdnjs.cloudflare.com');

        script.parentNode.removeChild(script);
        doc.write('<script src="' + src + '"></script>');
    }
})(document, window.jQuery || window.Zepto);
    • You can stick to a jQuery version by specifying it in the string
    • Perfect for Asset Management that doesn't work with HTML snips
    • Tested in the wild - works perfect for users from China
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  • 庸人自扰
    2020-11-21 08:00

    Using Razor syntax in ASP.NET, this code provides fallback support and works with a virtual root:

    @{var jQueryPath = Url.Content("~/Scripts/jquery-1.7.1.min.js");}
<script type="text/javascript">
    if (typeof jQuery == 'undefined')
        document.write(unescape("%3Cscript src='@jQueryPath' type='text/javascript'%3E%3C/script%3E"));
</script>

    Or make a helper (helper overview):

    @helper CdnScript(string script, string cdnPath, string test) {
    @Html.Raw("<script src=\"http://ajax.aspnetcdn.com/" + cdnPath + "/" + script + "\" type=\"text/javascript\"></script>" +
        "<script type=\"text/javascript\">" + test + " || document.write(unescape(\"%3Cscript src='" + Url.Content("~/Scripts/" + script) + "' type='text/javascript'%3E%3C/script%3E\"));</script>")
}

    and use it like this:

    @CdnScript("jquery-1.7.1.min.js", "ajax/jQuery", "window.jQuery")
@CdnScript("jquery.validate.min.js", "ajax/jquery.validate/1.9", "jQuery.fn.validate")
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  • 刺人心
    2020-11-21 08:02

    This seems to work for me:

    <html>
<head>
<script type="text/javascript" src="http://www.google.com/jsapi"></script>
<script type="text/javascript">
// has the google object loaded?
if (window.google && window.google.load) {
    google.load("jquery", "1.3.2");
} else {
    document.write('<script type="text/javascript" src="http://joecrawford.com/jquery-1.3.2.min.js"><\/script>');
}
window.onload = function() {
    $('#test').css({'border':'2px solid #f00'});
};
</script>
</head>
<body>
    <p id="test">hello jQuery</p>
</body>
</html>

    The way it works is to use the google object that calling http://www.google.com/jsapi loads onto the window object. If that object is not present, we are assuming that access to Google is failing. If that is the case, we load a local copy using document.write. (I'm using my own server in this case, please use your own for testing this).

    I also test for the presence of window.google.load - I could also do a typeof check to see that things are objects or functions as appropriate. But I think this does the trick.

    Here's just the loading logic, since code highlighting seems to fail since I posted the whole HTML page I was testing:

    if (window.google && window.google.load) {
    google.load("jquery", "1.3.2");
} else {
    document.write('<script type="text/javascript" src="http://joecrawford.com/jquery-1.3.2.min.js"><\/script>');
}

    Though I must say, I'm not sure that if this is a concern for your site visitors you should be fiddling with the Google AJAX Libraries API at all.

    Fun fact: I tried initially to use a try..catch block for this in various versions but could not find a combination that was as clean as this. I'd be interested to see other implementations of this idea, purely as an exercise.

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