The basic design idea and usage of jQuery is to select a web element and then do something with it. This is the fundamental feature that sets it apart from other Javascript libraries.

“One” selects the page element

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

  • The alternative expression can beCSS 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
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  • It can also beJquery-specific expressions:
$('a:first') // Select the first a element in the page$('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
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Two changes the result set

The second idea behind jQuery is to provide a variety of powerful filters to filter the structure 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
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Sometimes we need to start from a result set and move to a nearby related element. JQuery also provides a way to move around 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
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“Three” 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');
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Broken down, it looks like this:

$('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
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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 objects are created by jQuery functions and are elements corresponding to object operations.

JQuery also provides the.end() method, which allows the result set to take a step back:

$('div') .find('h3') .eq(2) .html('Hello') .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
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Operation of the “four” element

1. Value and assignment

The fourth design idea of jQuery is to use the same function for getters and setters. Whether to evaluate or assign depends on the parameters of the function. The overloaded

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

2. Mobile

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 way is to use.insertAfter(), move the div element after the p element:
$('div').insertAfter($('p'));
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  • The second way is to use.after()Add the p element to the front of the div element:
$('p').after($('div'));
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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

3. Create a

To create a new element, just pass it directly into jQuery’s constructor:

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

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().

“Five” Tools (Utility)

In addition to operating on selected elements, jQuery also provides some element-independent utility methods. You can use these methods directly without having to select the element.

Utility methods are methods defined on the jQuery constructor, jquery.method (), so they can be used directly. The methods that operate on elements are those defined on the constructor’s prototype object, jquery.prototype.method (), so you have to generate instances (that is, select elements) to use.

The following tools are commonly used:

$.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

“Six” event operation

The seventh design idea of jQuery is to tie events directly to web elements.

$('p').click(function(){ alert('Hello'); });Copy the code

Currently, jQuery supports the following events:

.blur() Form elements lose focus. .change() the value of the form element changes.click() mouse click.dblclick() mouse double-click.focus() the form element gets focus.focusin() child gets focus.focusout() child loses focus .hover() specifies a handler for both mouseenter and mouseleave events. Keydown () presses the keyboard (long button, returns only one event). Keypress () presses the keyboard (long button, returns only one event). Will return multiple events).keyup() release the key.load () element is loaded. Mousedown () press the mouse. Mouseenter () mouse entry (entering child elements does not trigger).mouseleave() Mouse away (leaving child element does not trigger). Mousemove () mouse moves inside the element. Mouseout () Mouse away (leaving child element also triggers) Resize () The size of the browser window changes. Scroll () the position of the scroll bar changes. Select () The user selects the content in the text box .toggle() runs multiple functions in sequence based on the number of mouse clicks. Unload () The user leaves the pageCopy the code

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Article content from: Ruan Yifeng jQuery design ideas

A handwritten jQuery implementation: github.com/MiaMou/dom-…