Available since v0.1.0

Fires on the native blur event (via focusout capture so it reaches the instrumented element). Use for validation and "user finished with this field" semantics.

Syntax

<input type="email"
  fs-assert="signup/validate-email"
  fs-trigger="blur"
  fs-assert-updated=".email-field[classlist=valid:true]">

When to use it

• Field-level validation that runs after the user leaves the field
• Save-on-blur semantics (inline edit, autosave)
• "Did the user actually finish?" gates on form sections

Example

<input type="text" name="username"
  fs-assert="signup/check-username"
  fs-trigger="blur"
  fs-assert-visible-available=".username-available"
  fs-assert-visible-taken=".username-taken">

Pairs well with

• fs-assert-updated — field marks itself valid/invalid
• fs-assert-visible — a validation message appears
• Conditional assertions — branch on available vs taken
• [value-matches=...] — verify the committed value via self-referencing

Gotchas

• Blur on text inputs also triggers change. If you have both a blur trigger and a change trigger on the same field, both fire when the user leaves. Pick one.
• Click-on-submit patterns lose focus. Clicking a submit button blurs the input — the blur assertion fires alongside the submit.

See also

• focus — the complementary trigger
• change — commit-semantics alternative
• Triggers index