JavaScript/TypeScript Rule Helper Functions

Helper functions are located in packages/analysis/src/jsts/rules/helpers/. These provide common utilities for rule implementations.

Helper Categories

• AST Utilities: Functions for traversing and querying the AST
• Type Checking: Helpers for checking types via TypeScript parser services
• Module Helpers: Functions for analyzing imports and exports
• String/Regex Utilities: Common string and pattern matching helpers

Common Helper Functions

• isCallingMethod() - Check if a call expression is calling a specific method
• getUniqueWriteUsageOrNode() - Track variable assignments
• isRequiredParserServices() - Check if TypeScript type information is available
• isArray(), isString(), etc. - Type checking helpers
• getImportDeclarations() - Get import declarations from the context

Usage Guidance

Before writing any new function, search packages/analysis/src/jsts/rules/helpers/ for an existing equivalent. Key files to check:

• ast.ts — generic AST utilities (child enumeration, node classification, ancestor walking)
• vue.ts — Vue-specific helpers
• react.ts — React/JSX-specific helpers

Reviewers will reject re-implementations of existing helpers.

Anti-pattern: Iterating Object.keys(node) to enumerate child nodes. Use the existing childrenOf helper instead:

// ❌ Do not do this
for (const key of Object.keys(node)) { ... }

// ✅ Use this
for (const child of childrenOf(node)) { ... }

If you write a new utility function that only operates on estree/TSESTree nodes with no rule-specific domain logic, place it in helpers/ast.ts (or helpers/vue.ts, helpers/react.ts for domain-specific utilities) — not inside the individual rule file. Functions buried in a rule file are invisible to future implementers.

Finding Helpers

To explore available helpers:

ls packages/analysis/src/jsts/rules/helpers/

Read helper implementations to understand their usage and parameters.

Helper Contracts

childrenOf

childrenOf(node) always returns estree.Node[]. Do not write custom type guard predicates or Array.isArray() checks on its return values — they are dead code:

// ❌ Redundant — childrenOf already guarantees estree.Node[]
for (const child of childrenOf(node)) {
  if (typeof child === 'object' && 'type' in child) { ... }
}

// ✅ Iterate directly
for (const child of childrenOf(node)) {
  // child is already estree.Node
}