# X_TEST_ISLAND_STATE_JSON_INVALID

## Means

an island state carries a value JSON does not

## Typical cause

island props ride the `data-x-props` script tag, which is `JSON.stringify`d — so a `Date`, a function, a `Map`, a cycle, a non-finite number or an `undefined` is not approximately right in the picture, it is a prop the component never receives. `cause` names the exact path

## Fix

write the value the cause names as JSON — a string, a number, a boolean, `null`, an array or a plain object

[Testing](/error-codes#testing)