> For the complete documentation index, see [llms.txt](https://radlohead.gitbook.io/typescript-deep-dive/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://radlohead.gitbook.io/typescript-deep-dive/overview/binder.md).

# Binder

Most JavaScript transpilers out there are simpler than TypeScript because they provide little in the way of code analysis. The typical JavaScript transpilers only have the following flow:

```typescript
SourceCode ~~Scanner~~> Tokens ~~Parser~~> AST ~~Emitter~~> JavaScript
```

While the above architecture is true as a simplified understanding of TypeScript js generation, a key feature of TypeScript is its *Semantic* system. In order to assist type checking (performed by the `checker`), the `binder` (in `binder.ts`) is used to connect the various parts of the source code into a coherent type system that can then be used by the `checker`. The main responsibility of the binder is to create *Symbols*.

## Symbol

Symbols connect declaration nodes in the AST to other declarations contributing to the same entity. Symbols are the basic building blocks of the Semantic system. The symbol constructor is defined in `core.ts` (and `binder` actually uses the `objectAllocator.getSymbolConstructor` to get its hands on it). Here is the symbol constructor:

```typescript
function Symbol(flags: SymbolFlags, name: string) {
    this.flags = flags;
    this.name = name;
    this.declarations = undefined;
}
```

`SymbolFlags` is a flag enum and is really used to identify additional classifications of the symbol (e.g. variable scope flags `FunctionScopedVariable` or `BlockScopedVariable` among others)

## Usage by Checker

The `binder` is actually used internally by the type `checker` which in turn is used by the `program`. The simplified call stack looks like:

```
program.getTypeChecker ->
    ts.createTypeChecker (in checker)->
        initializeTypeChecker (in checker) ->
            for each SourceFile `ts.bindSourceFile` (in binder)
            // followed by
            for each SourceFile `ts.mergeSymbolTable` (in checker)
```

The unit of work for the binder is a SourceFile. The `binder.ts` is driven by `checker.ts`.


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://radlohead.gitbook.io/typescript-deep-dive/overview/binder.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.