In the introduction to the attributes section, you saw an example showing how attributes are added to the opening tag. The example used the
<a> tag, but neither the element nor the specific attributes introduced in that example were discussed:
<a> anchor tag, along with the
href attribute, create a hyperlink. Links are the backbone of the internet. The first web page contained 25 links, reading "Everything there is online about W3 is linked directly or indirectly to this document." In all likelihood, everything there is online about W3 is linked directly or indirectly from this document too!
The power of the web, and the
<a> tag, have grown immensely since Tim Berners-Lee published this first explanation in August 1991. Links represent a connection between two resources, one of which is the current document. Links can be created by
<link>. You've learned about
<link>, and will discover forms in a separate section. There is also an entire form learn section. In this session, you'll find out about the single-letter, not-so-simple
href attribute #
While not required, the
href attribute is found in almost all
<a> tags. Providing the address of the hyperlink is what turns the
<a> into a link. The
href attribute is used to create hyperlinks to locations within the current page, other pages within a site, or other sites altogether. It can also be coded to download files or to send an email to a specific address, even including a subject and suggested email body content.
<a href="https://machinelearningworkshop.com">Machine Learning Workshop</a>
<a href="#teachers">Our teachers</a>
<a href="https://machinelearningworkshop.com#teachers">MLW teachers</a>
<a href="mailto:firstname.lastname@example.org">Email Hal</a>
<a href="tel:8005551212">Call Hal</a>
The first link includes an absolute URL, which can be used on any site in the world to navigate to the MLW home page. Absolute URLs include a protocol, in this case
https://, and a domain name. When the protocol is written simply as
//, it is an implicit protocol and means "use the same protocol as is currently being used."
Relative URLs do not include a protocol or domain name. They are "relative" to the current file. MLW is a single-page site, but this HTML series has several sections. In order to link from this page to the attributes lesson, a relative URL is used
The second link is just a link fragment identifier, and will link to the element with
id="teachers", if there is one, on the current page. Browsers also support two "top of page" links: clicking on
<a href="#top">Top</a> (case-insensitive) or simply
<a href="#">Top</a> will scroll the user to the top of the page, unless there is an element with the id of
top set in the same letter casing.
MLW is a fairly long document. To save scrolling, you can add a link back to the top from the bottom of the #teachers section:
<a href="#top">Go to top.</a>
The third link combines the two values: it contains an absolute URL followed by a link fragment. This enables linking directly to a section in the defined URL, in this case, the
#teachers section of the MLW home page. The MLW page will be loaded; then the browser will scroll to the teachers section without sending the fragment in the HTTP request.
href attribute can begin with
tel: to email or make calls, with the handling of the link depending on the device, operating system, and installed applications.
mailto link doesn't need to include an email address, but it can, along with
body text to prepopulate the email. By default, an email client will be opened. You could prepopulate the subject and body of the email with no email address, to allow site visitors to invite their own friends. In our link, in the footer of the document, we include the URL to the registration:
">Tell a machine</a>
The question mark (
?) separates the
mailto: and the email address, if any, from the query term. Within the query, ampersands (
&) separate the fields, and equal signs (=) equate each field name with its value. The entire string is percent-encoded, which is definitely necessary if the
href value isn't quoted or if the values include quotes.
Which app is opened when the user clicks on, taps, or hits Enter on a
tel link depends on the operating system, installed applications, and settings the user has on their device. An iPhone may open FaceTime, the phone app, or contacts. A Windows desktop might open Skype, if installed.
There are several other types of URLs, such as blobs and data URLs (see examples in the
download attribute discussion). For secure sites (those served over
https), it is possible to create and run app specific protocols with registerProtocolHandler().
When including links that are likely to open other installed applications, it's good to let the user know. Make sure the text between the opening and closing tags tells the user what type of link they're about to activate. CSS attribute selectors, such as
[href$=".pdf"] can be used to target styles by application type.
Downloadable resources #
download attribute should be included when the
href points to a downloadable resource. The value of the download attribute is the suggested filename for the resource to be saved in the user's local file system. SVGOMG, the SVG Optimizer, uses the
download attribute to suggest a file name for the downloadable blob that the optimizer creates. When
hal.svg is optimized, SVGOMG's download link opening tag is similar to:
<a href="blob:https://jakearchibald.github.io/944a5fc8-fdb3-458a-91ee-cdd5964b6646" download="hal.svg">
There's also a demo of a
<canvas> that creates a downloadable PNG data URL.
To link to a downloadable resource, include the URL of the asset as the value of the href attribute and the suggested filename that can be used in the user's file system as the value of the
Browsing context #
target attribute enables the defining of the browsing context for link navigation (and form submission. The four case-insensitive, underscore-prefixed keywords were discussed with the
<base> element. They include the default
_self, which is the current window,
_blank, which opens the link in a new tab,
_parent, which is the parent if the current link is nested in an object or iframe, and
_top, which is the top-most ancestor, especially useful if the current link is deeply nested.
_parent are the same as
_self if the link is not nested. The
target attribute is not limited to these four key terms: any term can be used.
Every browsing context—basically, every browser tab—has a browsing context name. Links can open links in the current tab, a new unnamed tab, or a new or existing named tab. By default, the name is the empty string. To open a link in a new tab, the user can right-click and select "Open in a new tab". Developers can force this by including
A link with
target="_blank" will be opened in a new tab with a null name, opening a new, unnamed tab with every link click. This can create many new tabs. Too many tabs. For example, if the user clicks on
<a href="registration.html" target="_blank">Register Now</a> 15 times, the registration form will be opened in 15 separate tabs. This problem can be fixed by providing a tab context name. By including the
targetattribute with a case-sensitive value—such as
<a href="registration.html" target="reg">Register Now</a>—the first click on this link will open the registration form in a new
reg tab. Clicking on this link 15 more times will reload the registration in the
reg browsing context, without opening any additional tabs.
rel attribute controls what kinds of links the link creates, defining the relationship between the current document and the resource linked to in the hyperlink. The attribute's value must be a space-separated list on one or more of the score of rel attribute values supported by the
nofollow keyword can be included if you don't want spiders to follow the link. The
external value can be added to indicate that the link directs to an external URL and is not a page within the current domain. The
help keyword indicates the hyperlink will provide context-sensitive help. Hovering over a link with this
rel value will show a help cursor rather than the normal pointer cursor. Don't use this value just to get the help cursor; use the CSS
cursor property instead. The
next values can be used on links pointing to the previous and next document in a series.
<link rel="alternative">, the meaning of <a
rel="alternative"> depends on other attributes. RSS feed alternatives will also include
type="application/atom+xml, alternative formats will include the
type attribute, and translations will include the
hreflang attribute. If the content between the opening and closing tags is in a language other than the main document language, include the
lang attribute. If the language of the hyperlinked document is in a different language, include the
In this example, we include the URL of the translated page as the value of the
href, rel="alternate" to indicate that it's an alternative version of a site; the
hreflang attribute provides the language of the translations:
<a href="/fr/" hreflang="fr-FR" rel="alternate" lang="fr-FR">atelier d'apprentissage mechanique</a>
<a href="/pt/" hreflang="pt-BR" rel="alternate" lang="pt-BR">oficina de aprendizado de máquina</a>
If the French translation is a PDF, you can provide the type attribute with the PDF MIME type of the linked resource. While the MIME type is purely advisory, informing the user that a link will open a document of a different format is always a good idea.
<a href="/fr.pdf" hreflang="fr-FR" rel="alternate" lang="fr-FR" type="application/x-pdf">atelier d'apprentissage mechanique (pdf).</a>
Tracking link clicks #
One way to track user interactions is to ping a URL when a link is clicked. The
ping attribute, if present, includes a space-separated list of secure URLs (which start with
https) that should be notified, or pinged, if the user activates the hyperlink. The browser sends
POST requests with the body
PING to the URLs listed as the value of the
User experience tips #
- Always consider the user experience when writing HTML. Links should provide enough information about the linked resource so the user knows what they are clicking on.
- Within a block of text, ensure the appearance of your links differs enough from the surrounding text so that users can easily identify links from the rest of the content, ensuring that color alone is not the only means of differentiating between text and the surrounding content.
- Always include focus styles; this enables keyboard navigators to know where they are when tabbing through your content.
- The content between the opening
</a>is the link's default accessible name and should inform the user of the link's destination or purpose. If the content of a link is an image, the
altdescription is the accessible name. Whether the accessible name comes from the
altattribute or a subset of words within a block of text, make sure it provides information about the link's destination. Link text should be more descriptive than "click here" or "more information"; this is important for your screen reader users and your search engine results!
- Don't include interactive content, such as a
<input>, inside a link. Don't nest a link within a
<label>either. While the HTML page will still render, nesting focusable and clickable elements inside interactive elements creates a bad user experience.
- If the
hrefattribute is present, pressing the Enter key while focused on the
<a>element will activate it.
- Links are not limited to HTML. The
aelement can also be used within an SVG, forming a link with either the 'href' or 'xlink:href' attributes.
links attribute returns an
area elements that have an
let a = document.links; // obtain the first link in the document
a.href = 'newpage.html'; // change the destination URL of the link
a.protocol = 'ftp'; // change just the scheme part of the URL
a.setAttribute('href', 'https://machinelearningworkshop.com/'); // change the attribute content directly
In this section, you have learned all about links. The next section covers lists, which we need to learn so we can group them together to create lists of links (also known as navigation).
What does the nofollow link do?Makes the link not clickable. Asks spiders not to follow the link. Makes your visit to the site untrackable.
Which links will take you to the top of the page?