> For the complete documentation index, see [llms.txt](https://gofast.disasm.dev/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://gofast.disasm.dev/built-in-visitors.md).

# Built In Visitors

The **go-fAST** ecosystem includes powerful built-in visitors designed for common patterns of AST analysis and transformation. These visitors encapsulate traversal logic and are ideal for optimization, resolution, and safe rewriting of JavaScript code.

These visitors conform to the `ast.Visitor` interface and can be embedded, extended, or used directly. 

***

### 🔄 Resolver Visitor

The `resolver` module walks the AST and performs **scope resolution** for:

* **Variable declarations and bindings**
* **Lexical scopes (functions, blocks)**
* **Identifier resolution and context tagging**

#### Use Case

Before performing operations that depend on lexical scoping (e.g. renaming, removing unused vars, or simplifying, you should run:

```go
resolver.Resolve(program)
```

#### What It Adds

* Each identifier is annotated with a **ScopeContext**, which is later used by tools like the `simplifier`
* Can be used to implement tools like dead code elimination or variable mangling

***

### 🧠 Simplifier Visitor

The `simplifier` module walks the AST and performs **semantic simplifications**:

* Constant folding (`1 + 2 -> 3`)
* Logical simplifications (`true && x -> x`)
* Literal optimizations (`'abc'.length -> 3`, `'abc'[0] -> 'a'`)
* Elimination of unnecessary sequence expressions

#### Example

```
data, _ := os.ReadFile("input.js")
ast, _ := parser.ParseFile(string(data))
simplifier.Simplify(ast, true) // also resolves scope
fmt.Println(generator.Generate(ast))
```

#### Benefits

* Safe reduction of redundant logic
* Prunes unnecessary expressions
* Handles tricky edge cases like `typeof`, `instanceof`, `NaN`, `undefined`, etc.
* Maintains runtime side-effects and correctness


---

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