> ## Documentation Index
> Fetch the complete documentation index at: https://docs.hasmcp.com/llms.txt
> Use this file to discover all available pages before exploring further.

# What is Goja (JS) Logic in HasMCP?

> Structuring complex data transformations natively via embedded JavaScript execution flexibly logically.

# What is Goja (JS) Interceptor Logic?

If JMESPath is considered the "Fast Slicer" for generic structural pruning, **Goja (JavaScript) Interceptors** are the full programmable processors internally deployed into the HasMCP orchestration proxy.

Goja is a pure Go implementation of ECMAScript 5.1(+). It allows API administrators to write explicit JavaScript functions that dynamically intercept and rewrite upstream payloads *before* they are returned to the final LLM Context Window.

### Why Use JavaScript?

While JMESPath is fantastic for extracting fields (`users[0].name`), it is entirely declarative. It **cannot**:

1. Mask or RegEx replace sensitive string formats safely (like wiping out the first 5 digits of an SSN).
2. Compute mathematical sums natively (looping an array to return a final `total_price`).
3. Conditionally mutate variables dynamically (`if account.balance < 0, inject boolean "is_bankrupt": true`).
4. Perform complex un-nesting natively, such as executing `Base64` decodes on internal payload rings.

### How It Connects to Tools

Inside the visual dashboard natively, you simply define the Javascript snippet inside the **Data Transformation** block of your specific Provider Tool explicitly.

Example formatting:

```javascript theme={null}
input.status = "Interpreted by HasMCP";
return input;
```

The string returned by the generic JS `intercept` function completely replaces the raw REST API buffer exclusively. Your LLM agent instantly receives the procedurally mapped outputs without recognizing the physical complexity seamlessly.