- Navigating a page with jQuery
jQuery is a lightweight, "write less, do more", JavaScript library.
The purpose of jQuery is to make it much easier to use JavaScript on your website.
jQuery takes a lot of common tasks that require many lines of JavaScript code to accomplish, and wraps them into methods that you can call with a single line of code.
jQuery also simplifies a lot of the complicated things from JavaScript, like AJAX calls and DOM manipulation.
The jQuery library contains the following features:
- HTML/DOM manipulation
- CSS manipulation
- HTML event methods
- Effects and animations
- AJAX
- Utilities
You can select elements in the DOM in exactly the same way as you can in your CSS by using tag, #id, .class, [attribute=""] and :pseudo selectors. Below are some examples.
- tag
$('div');
- class name:
$('.class-name');
- ID:
$('#id');
- attribute:
$('input[type="checkbox"]');
- pseudo selectors
$('.class-name:nth-of-type(3)');
$('.class-name:first-child()');
$('.class-name:last-child()');
jQuery also makes available some unique selectors that are only available within jQuery, this is called filtering, more on this below in traversing the DOM. But bare in mind that CSS selectors will always be quicker than jQuery selctors.
- To select the first element
$('.class-name').first();
- To select the last element
$('.class-name').last();
- To select the nth element, where N = number ( starting from 0 )
$('.class-name').eq(N);
Navigating the DOM is probably the most important thing to learn from a front-end development point of view. It's not always possible to directly select the element that you're trying to manipulate.
jQuery provides a variety of methods that allow us to traverse the DOM.
The largest category of traversal methods are tree-traversal.
With jQuery you can traverse up the DOM tree to find ancestors of an element.
An ancestor is a parent, grandparent, great-grandparent, and so on
Three useful jQuery methods for traversing up the DOM tree are:
.parent()
.parents()
.parentsUntil()
The .parent() method returns the direct parent element of the selected element.
This method only traverse a single level up the DOM tree.
The following example returns the direct parent element of each elements:
$(document).ready(function(){
$("span").parent();
});
The .parents() method returns all ancestor elements of the selected element, all the way up to the document's root element (<html>).
The following example returns all ancestors of all <span> elements:
$(document).ready(function(){
$("span").parents();
});
The .parentsUntil() method returns all ancestor elements between two given arguments.
The following example returns all ancestors of all elements that are <ul> elements:
$(document).ready(function(){
$("span").parentsUntil("div");
});
With jQuery you can traverse down the DOM tree to find descendants of an element.
A descendant is a child, grandchild, great-grandchild, and so on.
Two useful jQuery methods for traversing down the DOM tree are:
.children()
.find()
The .children() method returns all direct children of the selected element.
This method only traverses a single level down the DOM tree.
The following example returns all elements that are direct children of each <div> elements:
$(document).ready(function(){
$("div").children();
});
The following example returns all
elements with the class name "first", that are direct children of <div>:
You can also use an optional parameter to filter the search for children.
The following example returns all
elements with the class name "first", that are direct children of
$(document).ready(function(){
$("div").children("p.first");
});
The .find() method returns descendant elements of the selected element, all the way down to the last descendant.
$(document).ready(function(){
$("div").find("span");
});
With jQuery you can traverse sideways in the DOM tree to find siblings of an element.
Siblings share the same parent. Traversing Sideways in The DOM Tree
There are many useful jQuery methods for traversing sideways in the DOM tree:
.siblings().next().nextAll().nextUntil().prev().prevAll().prevUntil()
The .siblings() method returns all sibling elements of the selected element.
The following example returns all sibling elements of <h2>:
$(document).ready(function(){
$("h2").siblings();
});
You can also use an optional parameter to filter the search for siblings.
The following example returns all sibling elements of <h2> that are <p> elements:
$(document).ready(function(){
$("h2").siblings("p");
});
The .next() method returns the next sibling element of the selected element.
The following example returns the next sibling of <h2>:
$(document).ready(function(){
$("h2").next();
});
The .nextAll() method returns all next sibling elements of the selected element.
The following example returns all next sibling elements of <h2>:
$(document).ready(function(){
$("h2").nextUntil("h6");
});
The .prev(), .prevAll() and .prevUntil() methods work just like the methods above but with reverse functionality: they return previous sibling elements (traverse backwards along sibling elements in the DOM tree, instead of forward).
The .first(), .last(), .eq(), .filter() and not() Methods
The most basic filtering methods are .first(), .last() and .eq(), which allow you to select a specific element based on its position in a group of elements.
Other filtering methods, like .filter() and .not() allow you to select elements that match, or do not match, a certain criteria.
The .first() method returns the first element of the specified elements.
The .last() method returns the last element of the specified elements.
The .eq() method returns an element with a specific index number of the selected elements.
The index numbers start at 0, so the first element will have the index number 0 and not 1.
The .filter() method lets you specify a criteria. Elements that do not match the criteria are removed from the selection, and those that match will be returned.
The following example returns all <p> elements with class name "intro":
$(document).ready(function(){
$("p").filter(".intro");
});
The .not() method returns all elements that do not match the criteria.
Tip: The .not() method is the opposite of .filter().
The following example returns all <p> elements that do not have class name "intro":
$(document).ready(function(){
$("p").not(".intro");
});
For a full list of traversing methods please see the jQuery documentation Traversing