ast-types

ast-types is a mature library for working with JavaScript ASTs, offering a builder API and visitor pattern that's more elegant than manually constructing objects. The `namedTypes` checks and `builders` API are genuinely useful once you understand them. However, the developer experience falls short of modern standards.

The TypeScript definitions exist but are frustratingly incomplete. Autocomplete works for basic node types, but breaks down with complex traversals or when using `.check()` methods. You'll find yourself constantly referencing the Mozilla Parser API docs or the source code to understand what properties are available. Error messages when validation fails are cryptic—you get "invalid value" without clear indication of what's wrong or what the expected shape should be.

The documentation assumes deep familiarity with AST concepts and doesn't provide enough practical examples. The getting-started experience involves significant trial and error. For teams already invested in the recast/jscodeshift ecosystem, it's tolerable. For new projects, consider @babel/types which offers superior TypeScript support and clearer APIs.

ast-types is a foundational library for JavaScript AST manipulation that provides runtime type checking and validation for syntax tree nodes. It's particularly useful when building code transformation tools, linters, or codemods. The builder API prevents malformed AST construction, which from a security perspective helps avoid generating invalid code that could lead to unexpected behavior.

The library doesn't handle input validation in the security sense—it assumes you're working with parsed ASTs from trusted sources. There's no inherent protection against malicious input trees that could cause resource exhaustion through deeply nested structures. Error messages are descriptive for development but don't expose sensitive information, which is good. However, the lack of updates since 2020 is concerning for long-term maintenance, though the problem space is relatively stable.

For code transformation work, the type checking catches errors early that would otherwise manifest as subtle bugs in generated code. The API is verbose but predictable, making it easier to reason about code correctness in large codebases.

ast-types is a foundational library for working with JavaScript ASTs in build tools, codemods, and analysis pipelines. The builder API and validation system are elegant - you construct AST nodes with builders.foo() methods that validate structure at creation time. Memory footprint is reasonable since it's just working with plain objects plus validation metadata. Zero runtime dependencies means no transitive dependency hell.

The practical experience is mostly positive: visitor pattern support is clean, type definitions are comprehensive, and the namedTypes namespace makes type checking straightforward. Error messages when building malformed nodes are helpful enough to fix issues quickly. Performance is not a concern - validation overhead is negligible compared to parsing or transformation work.

The main friction point is the last release being from 2020, though the API surface is stable enough that this hasn't caused breaking issues. Documentation assumes you already understand AST structures - there's no hand-holding. No logging hooks or observability built in, but for a library operating on data structures, that's actually appropriate. It does one thing well without bloat.