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# expression

> Add a pattern-based response without an API call.

[ref-datamap]: /docs/server-sdks/reference/typescript/agents/data-map

[ref-functionresult]: /docs/server-sdks/reference/typescript/agents/function-result

Add a pattern-based response that does not require an API call. Expressions are
evaluated in order; the first matching pattern wins.

## **Parameters**

**`testValue`** `string` — required

Template string to test (e.g., `"${args.command}"`).

---

**`pattern`** `string | RegExp` — required

Regex pattern to match against the test value.

---

**`output`** `FunctionResult` — required

[FunctionResult][ref-functionresult] to return when the pattern matches.

---

**`nomatchOutput`** `FunctionResult`

Optional FunctionResult to return when the pattern does not match.

---

## **Returns**

[`DataMap`][ref-datamap] -- Self for method chaining.

## **Example**

```typescript {4}
import { DataMap, FunctionResult } from '@signalwire/sdk';

const dm = new DataMap('route_command');
dm.expression(
  '${args.command}',
  /play.*/,
  new FunctionResult('Playing file.'),
  new FunctionResult('Unknown command.'),
);
```

> Add a pattern-based response without an API call.