JQuery, released in 2006, is the longest-lived library on the front end to date and the most widely used library in the world. The basic design idea and usage of jQuery is to “select a web element and do something with it”. This is the fundamental feature that sets it apart from other Javascript libraries. The jQuery style, also known as the chained style, is essentially a constructor that doesn’t need to add new.

Usually we provide a global function

window.jQuery()
/ / short
window$=window.jQuery
Copy the code

To distinguish DOM objects from jQuery objects, we usually prefix DOM objects with el and jQuery objects with $

const eldiv1 = document.querSelector() / / the DOM object
const $div2 = $() / / the jQuery object
Copy the code

Select web elements

The first step in using jQuery is often to put a selection expression into the constructor jQuery() ($for short) and get the selected element.

Select expressions can be CSS selectors:

$(document) // Select the entire document object$('#myId') // Select the page element with ID myId$('div.myClass') // Select the div element whose class is myClass$('input[name=first]') // Select the input element whose name attribute is equal to first
Copy the code

It can also be a jquery-specific expression:

    $('a:first') // Select the first a element in the page$('tr:odd') // Select the odd rows of the table$('#myForm :input') // Select the input element in the form$('div:visible') // Select the visible div element$('div:gt(2)') // Select all div elements except the first three$('div:animated') // Select the div element that is currently animated
Copy the code

Changing the result set

The second design idea of jQuery is to provide a variety of powerful filters to filter the result set and narrow the selection.

$('div').has('p'); // Select the div element that contains the p element$('div').not('.myClass'); // Select the div element whose class is not equal to myClass$('div').filter('.myClass'); // Select the div element whose class equals myClass$('div').first(); // Select the first div element$('div').eq(5); // Select the sixth div element
Copy the code

From the result set, move to a nearby related element. JQuery provides a way to move in the DOM tree:

$('div').next('p'); // Select the first p element after the div element$('div').parent(); // Select the parent of the div element$('div').closest('form'); // Select the form parent element nearest the div$('div').children(); // Select all the children of div$('div').siblings(); // Select the sibling element of div
Copy the code

The chain operation

The third design idea of jQuery is that when you finally select a web element, you can perform a series of operations on it. All operations can be linked together in a chain form, such as:

$('div').find('h3').eq(2).html('Hello');
Copy the code

Break up the above statement:

$('div') // Find the div element.find('h3') // Select the h3 element.eq(2) // Select the third h3 element.html('Hello'); // Change its content to Hello
Copy the code

This is the most flattering and convenient feature of jQuery. It works because each step of the jQuery operation returns a jQuery object, so different operations can be linked together. JQuery provides the.end() method so that the result set can take a step back:

$('div') .find('h3') .eq(2) .html('Hello'). The end ()// Go back to the step where all h3 elements are selected.eq(0) // Select the first h3 element.html('World'); // Change its content to World
Copy the code

Operations on elements: value and assignment

The most common requirement for manipulating web elements is to get their values or assign them to them.

The fourth design idea of jQuery is to use the same function to complete the getter and setter, i.e. “valuer” and “assignment” in one. Whether to evaluate or assign depends on the parameters of the function.

$('h1').html(); // HTML () takes no arguments to fetch the value of h1$('h1').html('Hello'); // HTML () takes the argument Hello, which assigns h1
Copy the code

Common values and assignment functions are as follows:

.html() takes or sets the HTML content.text() Takes or sets the text content.attr() takes or sets the value of an attribute.width() Takes or sets the width of an element.height() Takes or sets the height of an element .val() retrieves the value of a form elementCopy the code

Note that if the result set contains more than one element, then all elements are assigned; Fetching only the value of the first element (except.text(), which fetches the text content of all elements).

Element operations: move

The fifth design idea of jQuery is to provide two sets of methods for manipulating the position of elements in a web page. One set of methods is to move the element directly, and the other set of methods is to move other elements so that the target element is where we want it to be.

Suppose we select a div element and need to move it after the P element.

The first method is to use.insertafter (), which moves the div element after the p element:

$('div').insertAfter($('p'));
Copy the code

The second way is to use.after(), which precedes the p element in the div:

$('p').after($('div'));
Copy the code

On the surface, the effect of the two methods is the same, the only difference seems to be the perspective of operation.

But in fact, there is one big difference between them, and that is that they return different elements.

The first method returns the div element, and the second method returns the P element. You can choose which method to use based on your needs.

There are four pairs of operation methods using this mode:

.insertafter () and.after() : inserts elements.insertbefore () and.before() : inserts elements.appendto () and.append() from the front outside the existing element. Inside the existing element, insert elements from behind. PrependTo () and. Prepend () : Inside the existing element, insert elements from the frontCopy the code

Operations on elements: copy, delete, and create

Copy elements using.clone().

Remove elements using.remove() and.detach(). The difference between the two is that the former does not retain the event of the deleted element, while the latter is retained for use when re-inserting the document.

Empty the element (but not delete it) using.empty().

Creating a new element is as simple as passing it directly into the jQuery constructor:

$('<p>Hello</p>'); $('<li class="new">new list item</li>'); $('ul').append('<li>list item</li>');
Copy the code

Common tool methods

$.trim() removes Spaces at both ends of the string. $.each() iterates over an array or object. $.inarray () returns the index position of a value in the array. If the value is not in the array, return -1. $.grep() returns the elements in the array that meet certain criteria. $.extend() merges multiple objects into the first object. $.makeArray() converts an object to an array. $.type() determines the class of objects (function objects, date objects, array objects, re objects, and so on). $.isarray () checks whether a parameter is an array. $.isemptyObject () determines whether an object is empty (without any attributes). $.isfunction () checks whether an argument is a function. $.isplainObject () determines whether a parameter is valid"{}"or"new Object"Object created. $.support() Checks whether the browser supports a feature.Copy the code

Excerpts from:

  1. Design Ideas of jQuery by Yifeng Ruan
  2. JQuery Design Ideas