Detailed explanation of jquery basic knowledge points

This time I will bring you a detailed explanation of the basic knowledge points of jquery. What are the precautions for using the basic knowledge points of jquery? The following is a practical case, let’s take a look.

jQuery is an excellent, lightweight js library that is compatible with CSS3 and various browsers (IE 6.0, FF1.5, Safari 2.0, Opera 9.0), and jQuery2.0 and subsequent This version will no longer support IE6/7/8 browsers. jQuery enables users to more easily process HTML (an application under Standard Universal Markup Language), events, implement animation effects, and easily provide AJAX interaction for websites. Another big advantage of jQuery is that its documentation is very complete, and various applications are also explained in detail, and there are many mature plug-ins to choose from.

1. The difference between jQuery entry function and Js entry function

[Note] js entry function refers to: window.onload = function (){};

Difference 1: Different writing numbers

The Js entry function can only appear once. If it appears multiple times, there will be an event coverage problem.

jQuery’s entry function can appear any number of times without event coverage.

Difference 2: Different execution timings

The Js entry function is executed after all file resources are loaded. These file resources include: page documents, external js files, external css files, pictures, etc.

The entry function of jQuery is executed after the document is loaded. The completion of document loading means: after the DOM tree is loaded, you can operate the DOM without waiting for all external resources to be loaded.

The order of document loading: from top to bottom, parsing and executing.

2. Mutual conversion between jQuery object and DOM object

①DOM object here refers to: using js The result returned by operating DOM

var btn = document.getElementById(“btnShow”); // btn就是一个DOM对象

②jQuery object here refers to: the result returned by using the method provided by jQuery to operate DOM

var $btn = $(“#btnShow”); // $btn就是一个jQuery对象

③DOM object converted into jQuery object

var $btn1 = $(btn); // 此时就把DOM对象btn转换成了jQuery对象$btn1
// $(document）.ready(function(){}); // 调用入口函数
// 此处是将document这个js的DOM对象，转换成了jQuery对象，然后才能调用jQuery提供的方法：ready

④Convert jQuery object into DOM object

// 第一种方式
var btn1 = $btn[0]; // 此时就把jQuery对象$btn转换成了DOM对象btn1 （推荐使用此方式）
// 第二种方式
var btn2 = $btn.get(0);// 此时就把jQuery对象$btn转换成了DOM对象btn2

3, jQuery selector

##Symbol (name) DescriptionUsage#ID selector.elementLevel selectorSpace>Children selector##Basic filtering Selector :eq(index)$(“li:eq(2)”).css(“color”, ”red”);:odd$("li:odd").css("color", "red"); with the id of j_wrap

Basic selector(Key points)
		$("#btnShow").css("color", "red"); Select the one with the id btnShow Element (the return value is a jQuery object, the same below)
	Class selector	$(“.liItem”).css(“color”, “red”); Select all elements containing class liItem
	Tag selector	$(“li”).css(“color”, “red”); Select the tag name For all elements of li
	Descendant selector	$(“#j_wrap li”).css(“color”, “red”); Select all descendant elements li of the element with id j_wrap
		$(“#j_wrap > ul > li”).css(“ color", "red"); Select all sub-elements ul of all sub-elements li of the element with id j_wrap
Selects an element with index number among the matched elements, and index is from Starting from 0		Select one of the li elements with index number 2 Element
Select all elements with odd index numbers among the matched elements, and the index starts from 0		Select all elements with odd index numbers in the li element
:even	Select all elements with even index numbers among the matched elements, and the index starts from 0	$("li:odd").css("color", "red"); Select all elements with even index numbers in the li element
Filter selector (method) (Key point)
find(selector)	Find all descendant elements of the specified element ( descendants)	$(“#j_wrap”).find(“li”).css(“color”, “red”); Select the one with the id j_wrap All descendant elements li
children()	Find the direct child elements (child elements) of the specified element	$ ("#j_wrap").children("ul").css("color","red"); Select all child elements ul
siblings()	Find all sibling elements (excluding self)	$("#j_liItem").siblings().css("color" , “red”); Select all sibling elements with id j_liItem
parent()	Find the parent element (parent )	$(“#j_liItem”).parent(“ul”).css(“color”,“red”); Select the parent element with id j_liItem
eq(index)	Find the index element of the specified element, index is the index number, starting from 0	$("li").eq(2).css("color", "red"); Select the second one among all li elements

I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the php Chinese website!

Recommended reading:

Detailed explanation of the overall architecture analysis and use of jquery

Detailed explanation of jQuery's method of judging the type and size of uploaded images

Detailed explanation of the use of jQuery framework

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