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anchor-is-valid

The HTML <a> element, with a valid href attribute, is formally defined as representing a hyperlink. That is, a link between one HTML document and another, or between one location inside an HTML document and another location inside the same document.

In fact, the interactive, underlined <a> element has become so synonymous with web navigation that this expectation has become entrenched inside browsers, assistive technologies such as screen readers and in how people generally expect the internet to behave. In short, anchors should navigate.

The use of JavaScript frameworks and libraries, like React, has made it very easy to add or subtract functionality from the standard HTML elements. This has led to anchors often being used in applications based on how they look and function instead of what they represent.

Whilst it is possible, for example, to turn the <a> element into a fully functional <button> element with ARIA, the native user agent implementations of HTML elements are to be preferred over custom ARIA solutions.

How do I resolve this error?

Case: I want to perform an action and need a clickable UI element

The native user agent implementations of the <a> and <button> elements not only differ in how they look and how they act when activated, but also in how the user is expected to interact with them. Both are perfectly clickable when using a mouse, but keyboard users expect <a> to activate on enter only and <button> to activate on both enter and space.

This is exacerbated by the expectation sighted users have of how buttons and anchors work based on their appearance. Therefore we find that using anchors as buttons can easily create confusion without a relatively complicated ARIA and CSS implementation that only serves to create an element HTML already offers and browsers already implement fully accessibly.

We are aware that sometimes anchors are used instead of buttons to achieve a specific visual design. When using the <button> element this can still be achieved with styling but, due to the meaning many people attach to the standard underlined <a> due its appearance, please reconsider this in the design.

Consider the following:

<a href="javascript:void(0)" onClick={foo} >Perform action</a>
<a href="#" onClick={foo} >Perform action</a>
<a onClick={foo} >Perform action</a>

All these anchor implementations indicate that the element is only used to execute JavaScript code. All the above should be replaced with:

<button onClick={foo} >Perform action</button>

Case: I want navigable links

An <a> element without an href attribute no longer functions as a hyperlink. That means that it can no longer accept keyboard focus or be clicked on. The documentation for no-noninteractive-tabindex explores this further. Preferably use another element (such as div or span) for display of text.

To properly function as a hyperlink, the href attribute should be present and also contain a valid URL. JavaScript strings, empty values or using only # are not considered valid href values.

Valid href attributes values are:

<a href="/some/valid/uri" >Navigate to page</a>
<a href="/some/valid/uri#top" >Navigate to page and location</a>
<a href="#top" >Navigate to internal page location</a>

Case: I need the HTML to be interactive, don't I need to use an a tag for that?

An <a> tag is not inherently interactive. Without an href attribute, it really is no different to a <div>.

Let's look at an example that is not accessible by all users:

<a
  className={'thing'}
  onMouseEnter={() => this.setState({showSomething: true})}>
  {label}
</a>

If you need to create an interface element that the user can click on, consider using a button:

<button
  className={'thing'}
  onClick={() => this.setState({showSomething: true})}>
  {label}
</button>

If you want to navigate while providing the user with extra functionality, for example in the onMouseEnter event, use an anchor with an href attribute containing a URL or path as its value.

<a
  href={someValidPath}
  className={'thing'}
  onMouseEnter={() => this.setState({showSomething: true})}>
  {label}
</a>

If you need to create an interface element that the user can mouse over or mouse out of, consider using a div element. In this case, you may need to apply a role of presentation or an interactive role. Interactive ARIA roles include button, link, checkbox, menuitem, menuitemcheckbox, menuitemradio, option, radio, searchbox, switch and textbox.

<div
  role="menuitem"
  className={'thing'}
  onClick={() => this.setState({showSomething: true})}>
  onMouseEnter={() => this.setState({showSomething: true})}>
  {label}
</div>

In the example immediately above an onClick event handler was added to provide the same experience mouse users enjoy to keyboard-only and touch-screen users. Never fully rely on mouse events alone to expose functionality.

References

  1. WebAIM - Introduction to Links and Hypertext
  2. Links vs. Buttons in Modern Web Applications
  3. Using ARIA - Notes on ARIA use in HTML

Rule details

This rule takes one optional object argument of type object:

{
    "rules": {
        "jsx-a11y/anchor-is-valid": [ "error", {
            "components": [ "Link" ],
            "specialLink": [ "hrefLeft", "hrefRight" ],
            "aspects": [ "noHref", "invalidHref", "preferButton" ]
          }]
    }
}

For the components option, these strings determine which JSX elements (always including <a>) should be checked for the props designated in the specialLink options (always including href). This is a good use case when you have a wrapper component that simply renders an <a> element (like in React):

// Link.js
const Link = props => <a {...props}>A link</a>;

...

// NavBar.js (for example)
...
return (
  <nav>
    <Link href="/home" />
  </nav>
);

For the aspects option, these strings determine which sub-rules are run. This allows omission of certain error types in restrictive environments.

  • noHref: Checks whether an anchor contains an href attribute.
  • invalidHref: Checks if a given href value is valid.
  • preferButton: Checks if anchors have been used as buttons.

The option can be used on its own or with the components and specialLink options.

If omitted, all sub-rule aspects will be run by default. This is the recommended configuration for all cases except where the rule becomes unusable due to well founded restrictions.

The option must contain at least one aspect.

Succeed

<a href="https://github.com" />
<a href="#section" />
<a href="foo" />
<a href="/foo/bar" />
<a href={someValidPath} />
<a href="https://github.com" onClick={foo} />
<a href="#section" onClick={foo} />
<a href="foo" onClick={foo} />
<a href="/foo/bar" onClick={foo} />
<a href={someValidPath} onClick={foo} />

Fail

Anchors should be a button:

<a onClick={foo} />
<a href="#" onClick={foo} />
<a href={"#"} onClick={foo} />
<a href={`#`} onClick={foo} />
<a href="javascript:void(0)" onClick={foo} />
<a href={"javascript:void(0)"} onClick={foo} />
<a href={`javascript:void(0)`} onClick={foo} />

Missing href attribute:

<a />
<a href={undefined} />
<a href={null} />

Invalid href attribute:

<a href="#" />
<a href={"#"} />
<a href={`#`} />
<a href="javascript:void(0)" />
<a href={"javascript:void(0)"} />
<a href={`javascript:void(0)`} />