How to detect if jquery is loaded

Method to detect whether jquery has been loaded: 1. Determine whether [jQuery()] is defined, the code is [if (jQuery) { jQuery has been loaded}]; 2. Determine whether [$()] is defined Definition, the code is [if(typeof jQuery == 'undefined'].

The operating environment of this tutorial: windows7 system, jquery2.1.4 version, DELL G3 computer .

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Method to detect whether jquery has been loaded:

After the current webpage loads jQuery, thejQuery()or$()function will be defined, so there are the following two methods to detect whether jQuery has been loaded:

Method 1:

if (jQuery) { // jQuery 已加载 } else { // jQuery 未加载 }

Method 2:

if (typeof jQuery == 'undefined') { // jQuery 未加载 } else { // jQuery 已加载 }

Remarks:

Above we check whether the jQuery function has been defined, which is a relatively safe and reliable method method, because when you load jQuery.js, you may load prototype.js or mootools.js, etc., which may redefine the$()function, and detecting whether the $() function exists will not Accurate.

We usually load jquery. If the bandwidth and speed are not very good, you can consider citing a third-party jquery

or

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