ARIA property
aria-valuenow
The value a range control currently holds.
It is the number people hear, and it has to change every time the control does. This is the spec's own example of a property that moves constantly, which is why the state and property labels are a poor guide to how much upkeep an attribute needs.
Which roles may carry aria-valuenow
- Value
- number
- Filed as
- A property, which is how ARIA files it and not a rule about how often it changes.
- Roles that inherit it
meter,progressbar,scrollbar,slider,spinbutton
Those lists are not advice. Browsers are required to ignore a non-global attribute sitting on a role that does not support it, so aria-valuenow on the wrong element is not weak, it is absent. You can read it in the DOM and nobody using a screen reader can.
Every role above comes from the specification's own list for this attribute, checked name for name. The normative definition stays with the W3C, in the aria-valuenow section of the ARIA specification.
Keeping aria-valuenow true
Leaving it out does not produce silence. On a slider, scrollbar or focusable separator the fallback is the exact midpoint between the minimum and the maximum, and on a meter it is the minimum. So a slider that never sets this announces as sitting precisely halfway along its range, with complete confidence, forever. Update it on every drag, every arrow key and every change your code makes on its own. And if aria-valuetext is present as well, that is what gets read instead, so the two have to move together or the number in the DOM stops being the number anybody hears.
How aria-valuenow gets checked
There are test rules that check an ARIA attribute is one that exists, is allowed on the role underneath it, and carries a value of the right type. What they map to is ARIA's own author requirements rather than any WCAG criterion, so a misplaced attribute breaks ARIA without being a WCAG failure by itself. It becomes one under 4.1.2 Name, Role, Value the moment the missing or wrong value means the control's state cannot be worked out programmatically, which is what usually happens next.
Nothing automated catches the failure this page is about. A stale value is a valid value, on a permitted role, with the right type. It is only wrong about the world.
Attributes you will meet alongside aria-valuenow
- aria-disabled Says a control is present but not available. Unlike the disabled attribute, it stays focusable, so people can still find out it is there.
- aria-errormessage Points at the message explaining why this field is invalid. Only meaningful while aria-invalid is set.
- aria-haspopup Says this control opens something, and what kind of thing it opens. A menu, a dialog, a listbox.
- aria-invalid Says a field's value has failed validation.
- aria-orientation Whether a widget runs horizontally or vertically, which decides which arrow keys move through it.
- aria-readonly The value can be read but not changed. Unlike disabled, it is still part of the form.
- aria-required Says a field has to be filled in before the form can be submitted.
- aria-valuemax The highest value a range control accepts.
Every ARIA state and property · Every ARIA role · ARIA explained