Pack declarations into parameters

Option: transforms.packDeclarationsIntoParameters

What it changes

Moves eligible leading var declarations with literal initializers into trailing default parameters.

function run() {
  var x = 1;
  return x;
}

function run(x = 1) {
  return x;
}

Run this transform by setting transforms.packDeclarationsIntoParameters to true:

obfuscate.mjs

const output = obfuscate(source, {
  transforms: {
    packDeclarationsIntoParameters: true,
  },
})

Open the TypeScript implementation on GitHub.

Review behavior checks and cases this transform leaves alone.

Last modified on August 26, 2026