# The TJS Language Why TJS exists, the principles it will not bend, its declarations and syntax, and the design notes behind the harder decisions — the reference half of the language, where the TJS section is the practical half. - [Why TJS](/why-tjs/) - [Design Principles & Invariants](/PRINCIPLES/) - [Declarations](/declarations/) - [TJS Syntax Reference](/TJS-SYNTAX/) - [Dictionary Defaults (Merge-on-Partial Object Arguments)](/dictionary-defaults/) - [Type identity: who answers "does this value satisfy this type?"](/type-identity/) - [Runtime fusion: what may be shared between TJS modules, and what may not](/runtime-fusion/) - [North star: JSON-Schema + predicates as the single source of truth for types](/type-system-north-star/) - [FunctionPredicate: Design Notes](/function-predicate-design/) - [Case study: fixing switch](/case-study-switch/) - [Small scoped parsers, not a rewrite](/parser-primitives/) - [Ambient Contracts — probe reality, derive verified predicate contracts](/ambient-contracts/) - [Native Engine Integration: TJS in V8 or JavaScriptCore](/native-engine-integration/) - [tjs-lang Technical Context](/CONTEXT/)