# ParamProperties

**Kind:** Interface

**Source:** [`packages/core/helpers/context-utils.ts`](https://github.com/nestjs/nest/blob/master/packages/core/helpers/context-utils.ts#L15)

**Part of:** [Core](subsystem-packages-core)

`ParamProperties` describes the metadata required to resolve a handler or controller parameter at runtime. It identifies the parameter position, its declared type, extraction configuration, optional transformation pipes, and the extractor responsible for obtaining the raw value.

## Properties

| Property | Type |
|---|---|
| `index` | `number` |
| `type` | `T | string` |
| `data` | `ParamData` |
| `pipes` | `PipeTransform[]` |
| `extractValue` | `IExtractor` |

## Diagram

```mermaid
graph LR
  A[Incoming request/context] --> B[IExtractor]
  B --> C[Extracted value]
  C --> D[PipeTransform[]]
  D --> E[Resolved parameter value]
  E --> F[Handler argument at index]
  
  G[ParamProperties] --> H[index: number]
  G --> I[type: T | string]
  G --> J[data: ParamData]
  G --> K[pipes: PipeTransform[]]
  G --> L[extractValue: IExtractor]
```

## Usage

```ts
import type { ParamProperties } from './context-utils';

const userIdParam: ParamProperties<string> = {
  index: 0,
  type: String,
  data: {
    name: 'id',
    source: 'params',
  },
  pipes: [parseIntPipe],
  extractValue: {
    extract(context, data) {
      return context.params[data.name];
    },
  },
};

// Runtime parameter resolution flow:
const rawValue = userIdParam.extractValue.extract(context, userIdParam.data);
const value = userIdParam.pipes.reduce(
  (result, pipe) => pipe.transform(result),
  rawValue,
);

handlerArguments[userIdParam.index] = value;
```

## AI Coding Instructions

- Use `index` as the authoritative position when assigning the resolved value into a handler argument array.
- Keep `extractValue` focused on reading raw values from the current execution context; apply validation and conversion through `pipes`.
- Preserve pipe order, since each `PipeTransform` should receive the output of the previous pipe.
- Use `data` to pass extractor-specific configuration such as parameter names, headers, query keys, or request-body paths.
- Support both constructor types and string-based types in `type`, especially when runtime type metadata may be unavailable.

## Relationships

- IMPORTS → `ParamData`
- IMPORTS → `PARAMTYPES_METADATA`
- IMPORTS → `RESPONSE_PASSTHROUGH_METADATA`
- IMPORTS → `ContextType`
- IMPORTS → `Controller`
- IMPORTS → `PipeTransform`
- IMPORTS → `Type`
- IMPORTS → `isFunction`