Checks whether jQuery. js has loaded judgment code.

Of course, this method is not limited to jQuery detection, and is common to any Javascript variables or functions.

After the current webpage loads jQuery, jQuery () or $ () functions will be defined, so there are two methods to check whether jQuery has been loaded:
Method 1:
Copy codeThe Code is as follows:
If (jQuery ){
// JQuery loaded
} Else {
// JQuery is not loaded
}


Method 2:
Copy codeThe Code is as follows:
If (typeof jQuery = 'undefined '){
// JQuery is not loaded
} Else {
// JQuery loaded
}

Note:
We have checked whether the jQuery function has been defined. This is a safe and reliable method, because when you load jQuery. after js, prototype may be loaded again. js or mootools. js and so on, where the $ () function may be redefined, and it will be inaccurate to check whether the $ () function exists.