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220 lines
4.5 KiB
Markdown
220 lines
4.5 KiB
Markdown
# jQuery Library
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## Including jQuery
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### Download and link the file
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```html
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<head>
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<script src="jquery-3.2.1.min.js"></script>
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</head>
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```
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### Use a CDN
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```html
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<head>
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<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
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</head>
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<!-- OR -->
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<head>
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<script src="https://ajax.aspnetcdn.com/ajax/jQuery/jquery-3.5.1.min.js"></script>
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</head>
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```
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### What is a CDN
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A **content delivery network** or **content distribution network** (CDN) is a large distributed system of servers deployed in multiple data centers across the Internet.
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The goal of a CDN is to serve content to end-users with high availability and high performance.
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CDNs serve a large fraction of the Internet content today, including web objects (text, graphics and scripts), downloadable objects (media files, software, documents), applications (e-commerce, portals), live streaming media, on-demand streaming media, and social networks.
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## HTML Manipulation
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### [Finding DOM elements](https://api.jquery.com/category/selectors/)
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```js
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$('tag');
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$("#id");
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$(".class");
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```
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### Manipulating DOM elements
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```js
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$("p").addClass("special");
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```
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```html
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<!-- before -->
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<p>Welcome to jQuery<p>
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<!-- after -->
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<p class="special">Welcome to jQuery<p>
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```
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### Reading Elements
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```html
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<a id="yahoo" href="http://www.yahoo.com" style="font-size:20px;">Yahoo!</a>
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```
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```js
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// find it & store it
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var link = $('a#yahoo');
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// get info about it
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link.html(); // 'Yahoo!'
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link.attr('href'); // 'http://www.yahoo.com'
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link.css('font-size'); // '20px
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```
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### Modifying Elements
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```js
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// jQuery
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$('a').html('Yahoo!');
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$('a').attr('href', 'http://www.yahoo.com');
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$('a').css({'color': 'purple'});
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```
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```html
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<!-- before -->
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<a href="http://www.google.com">Google</a>
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<!-- after -->
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<a href="http://www.yahoo.com" style="color:purple">Yahoo</a>
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```
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### Create, Store, Manipulate and inject
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```js
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let paragraph = $('<p class="intro">Welcome<p>'); // creat and store element
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paragraph.css('propery', 'value'); // manipulate element
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$("body").append(paragraph); // inject in DOM
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```
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### Regular DOM Nodes to jQuery Objects
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```js
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var paragraphs = $('p'); // an array
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var aParagraph = paragraphs[0]; // a regular DOM node
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var $aParagraph = $(paragraphs[0]); // a jQuery Object
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// can also use loops
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for(var i = 0; i < paragraphs.length; i++) {
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var element = paragraphs[i];
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var paragraph = $(element);
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paragraph.html(paragraph.html() + ' WOW!');
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}
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```
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## [Events](https://api.jquery.com/category/events/)
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```js
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var onButtonClick = function() {
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console.log('clicked!');
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}
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// with named callback & .on
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$('button').on('click', onButtonClick);
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// with anonymous callback & .on
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$('button').on('click', function(){
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console.log('clicked!');
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});
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// with .click & named callback
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$('button').click(onButtonClick);
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```
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### Preventing Default Event
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```js
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$('selector').on('event', function(event) {
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event.preventDefault();
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// custom logic
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});
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```
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## Plugins
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In the HTML, add a `<script>` ag that hotlinks to the CDN or source file:
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```html
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<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery-validate/1.17.0/jquery.validate.min.js"><script>
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```
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In the JavaScript call the jQuery puging on the DOM:
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```js
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$("form").validate();
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```
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**NOTE**: always link to the [minified](https://developers.google.com/speed/docs/insights/MinifyResources) js files.
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## More jQuery
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### Patters & Anti-Patterns
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```js
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// Pattern: name variables with $var
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$myVar =$('#myNode');
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// Pattern: store references to callback functions
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var callback = function(argument){
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// do something cool
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};
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$(document).on('click', 'p', myCallback);
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// Anti-pattern: anonymous functions
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$(document).on('click', 'p', function(argument){
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// do something anonymous
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});
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```
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### Chaining
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```js
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banner.css('color', 'red');
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banner.html('Welcome!');
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banner.show();
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// same as:
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banner.css('color', 'red').html('Welcome!').show();
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// same as:
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banner.css('color', 'red')
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.html('Welcome!')
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.show();
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```
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### DOM Readiness
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DOM manipulation and event binding doesn’t work if the `<script>` is in the `<head>`
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```js
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$(document).ready(function() {
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// the DOM is fully loaded
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});
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$(window).on('load', function(){
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// the DOM and all assets (including images) are loaded
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});
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```
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## AJAX (jQuery `1.5`+)
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```js
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$.ajax({
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method: 'POST',
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url: 'some.php',
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data: { name: 'John', location: 'Boston'}
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})
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.done(function(msg){alert('Data Saved: '+ msg);})
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.fail(function(jqXHR, textStatus){alert('Request failed: '+ textStatus);});
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```
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