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NG8109 means an Angular template interpolation references a signal without calling it. If the template should display the signal’s value, change {{ mySignal }} to {{ mySignal() }}. The check is one of Angular’s extended diagnostics and requires strictTemplates.
What NG8109 means
Angular names this diagnostic interpolatedSignalNotInvoked. It flags a signal that appears uninvoked in a text interpolation. A signal is a zero-argument function: calling it returns its current value. An interpolation therefore needs the call when it is meant to render that value.
For example, this component declares a signal holding a number:
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template: `<div>{{ mySignal() }}</div>`,
})
class MyComponent {
mySignal: Signal<number> = signal(0);
}How to fix NG8109
- Go to the template location identified by the diagnostic.
- Check whether the expression is a signal and the interpolation is meant to display its value.
- If so, invoke it by adding parentheses: change
{{ mySignal }}to{{ mySignal() }}.
Do not add parentheses indiscriminately in contexts where the signal object itself is intentionally being passed or used. NG8109 specifically concerns template interpolations.
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When Angular reports this diagnostic
Angular extended diagnostics require strictTemplates to be enabled; NG8109 has no additional requirement. Extended diagnostics are warnings by default. Angular lets a project configure an individual check or the default diagnostic category as a warning, an error, or suppressed.
Suppressing NG8109
If a project has a deliberate reason to silence this check, set its documented key in tsconfig.json:
{
"angularCompilerOptions": {
"extendedDiagnostics": {
"checks": {
"interpolatedSignalNotInvoked": "suppress"
}
}
}
}For the usual case, correcting the interpolation to call the signal addresses the cause rather than hiding the diagnostic.
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| Diagnostic | What it concerns |
|---|---|
| NG8109 | An uninvoked signal in a text interpolation. |
| NG8117 | An uninvoked ordinary function in a text interpolation. |
| NG8111 | An uninvoked function in an event binding. |
Use the diagnostic code and the expression’s type to identify which case you are dealing with; NG8109 is specifically about signals.
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Migration and Angular version notes
Angular’s v19 signal-input migration guidance describes an automated migration from @Input() fields to signal input() members that also updates references to call the migrated signal, including in templates. That guidance is specific to the v19 migration; do not assume its instructions apply unchanged to every Angular release.
Angular notes that new extended diagnostics may be added or enabled in minor versions. If a project treats the default warnings as errors, review Angular’s semver caveat when changing versions.
Quick Recap
Official Angular references
- NG8109: Signals must be invoked in template interpolations
- Angular extended diagnostics overview
- Angular compiler options
- Signal inputs migration guide
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