ifdef

xBuild v1 supports conditional code inclusion through // ifdef comment blocks, driven by the define object in xbuild.config.ts.

Enabling flags

Add a define object to the configuration:

export default {
    esbuild: {
        entryPoints: [ './src/main.ts' ],
        outdir: 'dist',
        format: 'esm',
        bundle: true
    },
    define: {
        DEBUG: true,      // includes ifdef DEBUG blocks
        FEATURE_X: false  // strips ifdef FEATURE_X blocks
    }
};

Syntax

Wrap the conditional code between // ifdef <FLAG> and // endif comments:

// main.ts

console.log('This code always runs');

// ifdef DEBUG
export function $$logger(...args: Array<unknown>): void {
    console.log(...args);
}
// endif

// ifdef FEATURE_X
console.log('Feature X is active');
// endif

$$logger('data'); // removed everywhere if $$logger does not exist

If the flag is truthy in define, the block stays (the ifdef/endif comments themselves are removed). If the flag is falsy or missing, the whole block is stripped from the output.

$$ function stripping

Functions and variables whose names start with $$ get special treatment: when their declaration is removed (for example because its ifdef block was stripped), every call site is removed too.

In the example above, when DEBUG is not set, both the $$logger declaration and the $$logger('data') call disappear - production builds stay clean without manual guards.

Class methods prefixed with $$ are stripped the same way.

WARNING

Only use $$ functions for side effects like logging or instrumentation. Code that consumes their return value will break when the definition is stripped.

See also

• define in the config reference
• Getting Started