> 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/ast/ast-tip-syntaxkind.md).

# TIP: SyntaxKind enum

`SyntaxKind` is defined as a `const enum`, here is a sample:

```typescript
export const enum SyntaxKind {
    Unknown,
    EndOfFileToken,
    SingleLineCommentTrivia,
    // ... LOTS more
```

It's a `const enum` (a concept [we covered previously](/typescript-deep-dive/type-system/enums.md)) so that it gets *inlined* (e.g. `ts.SyntaxKind.EndOfFileToken` becomes `1`) and we don't get a dereferencing cost when working with the AST. However, the compiler is compiled with `--preserveConstEnums` compiler flag so that the enum *is still available at runtime*. So in JavaScript you can use `ts.SyntaxKind.EndOfFileToken` if you want. Additionally you can convert these enum members to display strings using the following function:

```typescript
export function syntaxKindToName(kind: ts.SyntaxKind) {
    return (<any>ts).SyntaxKind[kind];
}
```


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