babel-dead-code-elimination - npm Package Versions

d4690c2: Do not eliminate empty object/array pattern function parameters

Function parameters are not dead code

3cf19e5: Fix: do not check function expressions for referenced variables

Function expressions do not add their names to outer scopes

5149b08: Do not eliminate arrow expressions

Arrow expressions do not add names to the outer scope. Arrow expressions bound to names via variable declarators are already handled by VariableDeclarator visitor.

86af914: Do not eliminate unreferenced variables from array patterns and object patterns when they do not match the provided candidates

Previously, the candidates were passed in to deadCodeElimination were not consulted when removing unreferenced variables from within patterns. This was a bug and has now been fixed.

ade9eee: Fix: do not eliminate function expressions

Function expressions do not add their names to outer scope, so they should never be dead code eliminated

bd5e331: Fix elimination for object patterns and array patterns

Previously, running dead code elimination on object patterns and array patterns (aka destructuring) was brittle. For example:

const {
  a: { b: c },
} = z
console.log(c)

Dead code elimination used to incorrectly remove the entire variable declaration even though c is referenced:

-const {
-  a: { b: c },
-} = z
 console.log(c);

This was caused by erroneous detection of a and b as unreferenced variables. But a and b are not variables, they are object property keys. Only c is a variable and it is referenced.

This is now corrected so that variables in object patterns and array patterns are detected only within values of object properties. This also correctly accounts for cases where the key and value are the same for example { a }.

8264d19: Initial release

deadCodeElimination

Eliminates unused code from the Babel AST by repeatedly removing unreferenced identifiers.

deadCodeElimination(ast)

findReferencedIdentifiers

Find identifiers that are currently referenced in the Babel AST.

Useful for limiting deadCodeElimination to only eliminate newly unreferenced identifiers, as a best effort to preserve any intentional side-effects in the source.

let ast = parse(source, { sourceType: "module" })
let referenced = findReferencedIdentifiers(ast)

traverse(ast, {
  /* ... your custom transform goes here ... */
})

deadCodeElimination(ast, referenced)