function

bundle.feature

function feature(

flag: string

): boolean;

Checks whether a feature flag is enabled at compile time.

At bundle time, Bun replaces each call with a boolean literal (true or false) and removes the unreachable branch.

@param flag

Name of the feature flag to check

@returns

true if the flag was passed with --feature=FLAG, false otherwise

import { feature } from "bun:bundle";

// With --feature=DEBUG, this becomes: if (true) { ... }
// Without --feature=DEBUG, this becomes: if (false) { ... }
if (feature("DEBUG")) {
  console.log("Debug mode enabled");
}