ifdef-loader

Webpack loader that allows JavaScript or TypeScript conditional compilation (#if ... #else ... #endif) directly from Webpack.

Conditional compilation directives are written inside /// triple slash comment so that they don't effect normal JavaScript or TypeScript parsing.

Example:

/// #if DEBUG
console.log("there's a bug!");
/// #endif

The DEBUG or any other variable can be specified when configuring the Webpack loader (see below).

The directive #if accepts any valid JavaScript expression:

/// #if PRODUCTION && version.charAt(0)=='X'
console.log("Ho!");
/// #endif

If the expression is true the block of code between #if and #endif is included, otherwise is excluded by commenting it out.

The #if clauses can also be nested:

/// #if PRODUCTION
      /// #if OS=="android"
      android_code();
      /// #endif
      /// #if OS=="ios"
      ios_code();
      /// #endif
/// #endif

Additionally, #else clauses can be defined for every #if clause:

/// #if PRODUCTION
console.log('Production!');
/// #else
console.log('Something else!');
/// #endif

Installation

In webpack build directory:

npm install ifdef-loader --save-dev

Configuration

Example of use with TypeScript files, enabling the DEBUG and version variables:

In webpack.config.json chain it before ts-loader:

// define preprocessor variables
const opts = {
   DEBUG: true,
   version: 3,
   "ifdef-verbose": true        // add this for verbose output
   "ifdef-triple-slash": false  // add this to use double slash comment instead of default triple slash
};

// pass as JSON object into query string ?json=...
const q = require('querystring').encode({json: JSON.stringify(opts)});

//...
{ test: /\.tsx?$/, exclude: /node_modules/, loaders: [ "ts-loader", `ifdef-loader?${q}` ] }
//...

in example.ts:

/// #if DEBUG
     /* code to be included if DEBUG is defined */
///   #if version <2
        /* code to be included if DEBUG is defined and version < 2*/
///   #endif
/// #endif

License

MIT

Contributions

Contributions in the form of issues or pull requests are welcome.

Changes

• v1.0.0 changed to triple slash comment syntax. Double slash syntax deprecated and available by turning off the ifdef-triple-slash option.

• v1.0.3 fixed bug occurring with short lines. Improved handling of line termination (CRLF vs LF) in order to preserve source maps.

• v1.1.0 added support for #else clauses.