Does jquery need $ to initialize?

jQuery is one of the commonly used JavaScript libraries in web development. It provides rich DOM operations, event processing, animation effects and other functions, allowing developers to write efficient JavaScript codes more simply and quickly. As the core of jQuery, $ (or jQuery) is an essential tool. So, does jquery need $ for initialization?

The answer is yes. Before using jquery, you must first initialize jquery in a certain way so that the $ or jQuery variable points to the jQuery object.

Generally speaking, we can initialize jQuery through the following code:

$(document).ready(function(){
   // jQuery初始化代码
});

In the above code, $(document).ready() is the most common jQuery initialization method. The function is to wait for the document to be fully loaded before running the initialization code to ensure that these elements already exist in the document before operating on DOM elements. Additionally, to prevent $ from being confused with other libraries, we can use the noConflict method to convert $ to a new variable name.

var jq = $.noConflict();

This code converts the original $ variable into jq, so that jq can be used instead of $ in the code to avoid conflict with $ variables of other libraries.

In addition to the above methods, there are also the following jQuery initialization methods:

1. Use jQuery objects directly

jQuery(document).ready(function(){
   // jQuery初始化代码
});

2. Abbreviation method

$(function(){
   // jQuery初始化代码
});

3. Run independently

(function($){
   //  jQuery初始化代码
}(jQuery));

This method is equivalent to passing jQuery as a parameter to a function, thus turning it into a closure. Among them, the $ variable is passed in as a parameter and can be redefined within the function body without affecting the $ variable in the global scope.

To sum up, in order to use jQuery correctly and avoid confusion with other libraries, after introducing the library file, $ or jQuery must be initialized so that it points to the jQuery object. There are many ways to initialize, and we should choose the method that suits us according to the actual situation.

jQuery type detection
In jQuery development, it is often necessary to determine the type of a variable. Generally speaking, you can use the typeof operator to get the type of a variable, but for jQuery objects, the return value of typeof is object, so accurate judgment cannot be made.

In response to this problem, jQuery provides a custom function that can determine whether a variable is a jQuery object. This function is called isJqueryObject, and its code is as follows:

function isJqueryObject(obj){
   return obj instanceof jQuery;
}

In this function, we use the instanceof operator in JavaScript to determine whether obj is an instance of the jQuery type.

In addition to the isJqueryObject function, jQuery also provides some other type detection functions, such as isNumeric(), isPlainObject(), etc. These functions can help us judge the data type more conveniently. For specific usage methods, please view the official documentation.

Summary
In jQuery, $ is a core variable whose function is to point to the jQuery object. Before using jQuery, you must initialize $ or jQuery so that it points to the jQuery object, otherwise you cannot use the functions and methods provided by jQuery. At the same time, in order to prevent $ from being confused with other libraries, after introducing the library file, you can use the noConflict function to convert $ to other variable names to avoid variable conflicts. In addition to the initialization of $, jQuery also provides some type detection functions that can help us judge the data type more conveniently.

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