Skip to content

nippur72/ifdef-loader

master
Switch branches/tags

Name already in use

A tag already exists with the provided branch name. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Are you sure you want to create this branch?
Code

Latest commit

 

Git stats

Files

Permalink
Failed to load latest commit information.
Type
Name
Latest commit message
Commit time
 
 
 
 
 
 
 
 
 
 

ifdef-loader

Webpack loader that allows JavaScript or TypeScript conditional compilation (#if ... #elif ... #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.

Additionally, #elif and #else clauses can be added to an #if clause:

/// #if env == 'PRODUCTION'
console.log('Production!');
/// #elif env == 'DEBUG'
console.log('Debug!');
/// #else
console.log('Something else!');
/// #endif

The #if clauses can also be nested:

/// #if PRODUCTION
      /// #if OS=="android"
      android_code();
      /// #elif OS=="ios"
      ios_code();
      /// #endif
/// #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 put ifdef-loader after ts-loader so that files are processed before going into TypeScript compiler:

// 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
   "ifdef-fill-with-blanks": true         // add this to remove code with blank spaces instead of "//" comments
   "ifdef-uncomment-prefix": "// #code "  // add this to uncomment code starting with "// #code "
};

/* ... */ { 
   test: /\.tsx?$/, 
   exclude: /node_modules/, 
   use: [
      { loader: "ts-loader" }, 
      { loader: "ifdef-loader", options: opts } 
   ]
}

// alternatively, options can be passed via query string:
const q = require('querystring').encode(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

Code in comments

Often times writing #if ... #else ... #endif results in code that is not syntactically valid or does not pass the LINT check. A possible workaround is to hide such code in comments and let ifdef-loader uncomment it if it's part of the block that has to be included in the output.

Example:

The following code is invalid because the linter sees a double declaration of the a variable.

// #if DEBUG
let a=1;
// #else
let a=2;
// #endif

Using code in comments:

// #if DEBUG
let a=1;
// #else
// #code let a=2;
// #endif

The code is now under comment so it's ignored by the linter; but it's uncommented by ifdef-loader if the else branch has to be included in the output (that is when DEBUG==false).

The // #code string prefix can be changed and has to be explictly specified in the options object:

const opts = {
   // ...
   "ifdef-uncomment-prefix": "// #code ",
   // ...
};

License

MIT

Contributions

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

Changes

  • v2.3.0 added option uncomment-prefix to write code in comments allowing it to pass through linters and syntax checking

  • v2.2.0 added option fill-with-blanks for removing code with blank spaces instead of // comments

  • v2.1.0 added support for #elif clause.

  • v2.0.0 BREAKING CHANGE: options are now passed using the standard Webpack API (loader-utils). See below for the upgrade.

  • 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.

Upgrading from v1 to v2

In v2 options are passed differently than v1, so you need to update your webpack.config.js. Just do the following simple changes:

/* from */ const q = require('querystring').encode({json: JSON.stringify(opts)});
/* to   */ const q = require('querystring').encode(opts);
/* you can keep the  ... `ifdef-loader?${q}` ... syntax    */
/* but it's better to pass options directly (see the docs) */

About

Webpack loader for JavaScript/TypeScript conditional compilation.

Resources

Stars

Watchers

Forks

Releases

No releases published

Packages

No packages published