var-to-let-const-js

Name: var-to-let-const-js codemod
Availability: InStock

Converts var declarations to const or let in JavaScript/JSX files, choosing
const when a variable is never reassigned and let when it is.

Installation

bash

var x = 1; where x is never reassigned → const x = 1;
var x = 1; x = 2; → let x = 1;
var x, y = 2; with mixed reassignment → split into separate let/const
statements, preserving declaration order (JS doesn't allow mixing keywords
in one var statement).
for (var i = 0; i < n; i++) → for (let i = 0; ...) (the counter is
reassigned by the increment).
for (var x of iterable) / for (var x in obj) → for (const x of ...)
unless x is reassigned inside the loop body, in which case let.
x++, x--, x += 1, and other compound assignments count as
reassignment.

**/*.{js,jsx,mjs,cjs}, excluding node_modules, dist, and build
(see workflow.yaml).

Already let/const: left untouched.
var accessed outside its declaring block: if a var is declared
inside an if/for/while/switch/try/catch block but read or
written outside that block within the same function, it's left as var
— converting it would change behavior, since let/const are
block-scoped while var is function-scoped.
Redeclared var: if the same name is declared with var more than
once in the same function/program scope, both declarations are left as
var (repeating a let/const declaration is a SyntaxError).
Shadowing across scopes (e.g. the same name declared in an outer
scope and independently in a nested function) is analyzed and converted
independently per scope — that's not a redeclaration.

This codemod does not target TypeScript (.ts/.tsx) files; the registry
already has var-to-let-const for that.

bash

MIT