检查是否使用 Javascript 加载了 jquery
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Checking if jquery is loaded using Javascript
提问by SoftwareSavant
I am attempting to check if my Jquery Library is loaded onto my HTML page. I am checking to see if it works, but something is not right. Here is what I have:
我正在尝试检查我的 Jquery 库是否已加载到我的 HTML 页面上。我正在检查它是否有效，但有些不对劲。这是我所拥有的：
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<script type="text/javascript" src="/query-1.6.3.min.js"></script>
<script type="text/javascript">
$(document).ready(function(){
if (jQuery) {
// jQuery is loaded
alert("Yeah!");
} else {
// jQuery is not loaded
alert("Doesn't Work");
}
});
</script>
回答by BoltClock
something is not right
有什么不对的
Well, you are using jQuery to check for the presence of jQuery. If jQuery isn't loaded then $()won't even run at all and your callback won't execute, unless you're using another library and that library happens to share the same $()syntax.
好吧，您正在使用 jQuery 来检查 jQuery 的存在。如果 jQuery 未加载，则$()根本不会运行，并且您的回调也不会执行，除非您使用另一个库并且该库碰巧共享相同的$()语法。
Remove your $(document).ready()(use something like window.onloadinstead):
删除你的$(document).ready()（改用类似的东西window.onload）：
window.onload = function() {
if (window.jQuery) {
// jQuery is loaded
alert("Yeah!");
} else {
// jQuery is not loaded
alert("Doesn't Work");
}
}
回答by Tushar Shukla
As per thislink:
根据这个链接：
if (typeof jQuery == 'undefined') {
// jQuery IS NOT loaded, do stuff here.
}
there are a few more in comments of the link as well like,
链接的评论中还有一些，例如，
if (typeof jQuery == 'function') {...}
//or
if (typeof $== 'function') {...}
// or
if (jQuery) {
alert("jquery is loaded");
} else {
alert("Not loaded");
}
Hope this covers most of the good ways to get this thing done!!
希望这涵盖了完成这件事的大多数好方法！！
回答by Niko
if ('undefined' == typeof window.jQuery) {
// jQuery not present
} else {
// jQuery present
}
回答by Alexein
You can do this fast on the console-tab when inspecting your webpage.
检查网页时，您可以在控制台选项卡上快速执行此操作。
E.g:
例如：
$ === jQuery
If it returns trueit means it's loaded.
如果它返回，true则表示它已加载。
回答by Nika Tsilosani
Just a small modification that might actually solve the problem:
只是一个可能真正解决问题的小修改：
window.onload = function() {
if (window.jQuery) {
// jQuery is loaded
alert("Yeah!");
} else {
location.reload();
}
}
Instead of $(document).Ready(function()use window.onload = function().
而不是$(document).Ready(function()使用window.onload = function().
回答by V.Volkov
If jQueryis loading asynchronously, you can wait till it is defined, checking for it every period of time:
如果jQuery是异步加载，你可以等到它被定义，每一段时间检查一次：
(function() {
var a = setInterval( function() {
if ( typeof window.jQuery === 'undefined' ) {
return;
}
clearInterval( a );
console.log( 'jQuery is loaded' ); // call your function with jQuery instead of this
}, 500 );
})();
This method can be used for any variable, you are waiting to appear.
此方法可用于任何变量，您正在等待出现。
回答by Bharadwaj
You can just type
window.jQueryin Console . If it return a function(e,n) ... Then it is confirmed that the jquery is loaded and working successfully.
您只需输入
window.jQueryConsole 即可。如果它返回一个函数（e，n）......然后确认jquery已加载并成功运行。
回答by Jajikanth pydimarla
A quick way is to run a jQuery command in the developer console. On any browser hit F12 and try to access any of the element .
一种快速的方法是在开发人员控制台中运行 jQuery 命令。在任何浏览器上点击 F12 并尝试访问任何元素。
$("#sideTab2").css("background-color", "yellow");
