vue

Invalid watch source in Composition API

watch.*is not a function|watch source.*invalid

Fixes

1.Pass a ref, reactive object, or getter function as watch source
2.Wrap plain values in () => value getter function
3.Don't pass .value — pass the ref itself to watch()

vuewatchcomposition-api

Related Errors

Cannot read property of undefined in setup()

Cannot read propert(y|ies) of undefined.*setup

•Initialize reactive refs before accessing nested properties
•Add optional chaining (?.) when accessing potentially undefined objects

Computed property getter returns undefined

computed property.*getter.*undefined

•Ensure computed getter always returns a value
•Check that reactive dependencies are initialized before computed runs

Direct prop mutation warning

Avoid mutating a prop directly

•Use a local data/ref copy of the prop instead of mutating directly
•Emit an event to let the parent update the prop value