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

# Checker

以前に述べたように\_checker\_は、TypeScriptを他のJavaScriptトランスパイラよりもユニークに強力にするものです。Checkerは`checker.ts`にあり、この時点ではTypeScriptの23k+行(コンパイラの最大部分)です。

## Programによる使用方法

`checker`は`program`により初期化されます。以下はコールスタックのサンプルです(`binder`で見たものと同じです)：

```
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)
```

## Emitterとの関連付け

`getDiagnostics`が呼び出されると、本当の型チェックが行われます。この機能は、例えば、`Program.emit`が一度要求されると、Checkerは`EmitResolver`を返します(ProgramはCheckerの`getEmitResolver`関数を呼び出します)。これは単に`createTypeChecker`のローカル関数の集合です。Emitterを見るときにこれについて再び言及します。

`checkSourceFile`(`createTypeChecker`のローカル関数)の下のコールスタックは以下の通りです。

```
program.emit ->
    emitWorker (program local) ->
        createTypeChecker.getEmitResolver ->
            // First call the following functions local to createTypeChecker
            call getDiagnostics ->
                getDiagnosticsWorker ->
                    checkSourceFile

            // then
            return resolver
            (already initialized in createTypeChecker using a call to local createResolver())
```


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