# isDefined

```ts
import { isDefined } from 'cx/util';
```


Type guard that checks if a value is not `undefined`. Note: `null` is considered defined.

## Signature

```ts
function isDefined<T>(value: T | undefined): value is T
```

## Examples

```ts
isDefined("hello");        // true
isDefined(0);              // true
isDefined(false);          // true
isDefined(null);           // true (null is defined)
isDefined(undefined);      // false
isDefined(void 0);         // false
```

## Use Cases

```ts
function getConfig(options?: { timeout?: number }) {
  if (isDefined(options?.timeout)) {
    // Use the provided timeout
    return { timeout: options.timeout };
  }
  // Use default
  return { timeout: 5000 };
}
```

## See Also

- [coalesce](/docs/utilities/coalesce) - Return first non-null value
- [isUndefined](/docs/utilities/is-defined) - Opposite check