unplugin-preprocessor-directives

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Install

npm i unplugin-preprocessor-directives

// vite.config.ts
import PreprocessorDirectives from 'unplugin-preprocessor-directives/vite'

export default defineConfig({
  plugins: [
    PreprocessorDirectives({ /* options */ }),
  ],
})

Example: playground/

// rollup.config.js
import PreprocessorDirectives from 'unplugin-preprocessor-directives/rollup'

export default {
  plugins: [
    PreprocessorDirectives({ /* options */ }),
  ],
}

// webpack.config.js
module.exports = {
  /* ... */
  plugins: [
    require('unplugin-preprocessor-directives/webpack')({ /* options */ })
  ]
}

// nuxt.config.js
export default defineNuxtConfig({
  modules: [
    ['unplugin-preprocessor-directives/nuxt', { /* options */ }],
  ],
})

This module works for both Nuxt 2 and Nuxt Vite

// vue.config.js
module.exports = {
  configureWebpack: {
    plugins: [
      require('unplugin-preprocessor-directives/webpack')({ /* options */ }),
    ],
  },
}

// esbuild.config.js
import { build } from 'esbuild'
import PreprocessorDirectives from 'unplugin-preprocessor-directives/esbuild'

build({
  plugins: [PreprocessorDirectives()],
})

// rspack.config.js
module.exports = {
  plugins: [
    require('unplugin-preprocessor-directives/rspack')({ /* options */ }),
  ],
}

Usage

Defining symbols

You use the following two preprocessor directives to define or undefine symbols for conditional compilation:

• #define: Define a symbol.
• #undef: Undefine a symbol.

You use #define to define a symbol. When you use the symbol as the expression that's passed to the #if directive, the expression will evaluate to true, as the following example shows:

// #define VERBOSE

// #if VERBOSE
console.log('Verbose output version')
// #endif

Conditional compilation

• #if: Opens a conditional compilation, where code is compiled only if the specified symbol is defined and evaluated to true.
• #elif: Closes the preceding conditional compilation and opens a new conditional compilation based on if the specified symbol is defined and evaluated to true.
• #else: Closes the preceding conditional compilation and opens a new conditional compilation if the previous specified symbol isn't defined or evaluated to false.
• #endif: Closes the preceding conditional compilation.

[!NOTE] By default, use vite's loadEnv function to load environment variables based on process.env.NODE_ENV and compile symbols as conditions.

// src/index.ts

// #if DEV
console.log('Debug version')
// #endif

// #if !MYTEST
console.log('MYTEST is not defined or false')
// #endif

You can use the operators == (equality) and != (inequality) to test for the bool values true or false. true means the symbol is defined. The statement #if DEBUG has the same meaning as #if (DEBUG == true). You can use the && (and), || (or), and ! (not) operators to evaluate whether multiple symbols have been defined. You can also group symbols and operators with parentheses.

class MyClass {
  constructor() {
    // #if (DEBUG && MYTEST)
    console.log('DEBUG and MYTEST are defined')
    // #elif (DEBUG==false && !MYTEST)
    console.log('DEBUG and MYTEST are not defined')
    // #endif
  }
}

Error and warning and info messages

You instruct the compiler to generate user-defined compiler errors and warnings and informational messages.

• #error: Generates an error.
• #warning: Generates a warning.
• #info: Generates an informational message.

// #error this is an error message
// #warning this is a warning message
// #info this is an info message

Custom directive

You can used defineDirective to define your own directive.

Taking the built-in directive as an example:

export const MessageDirective = defineDirective<MessageToken, MessageStatement>(context => ({
  lex(comment) {
    return simpleMatchToken(comment, /#(error|warning|info)\s*(.*)/)
  },
  parse(token) {
    if (token.type === 'error' || token.type === 'warning' || token.type === 'info') {
      this.current++
      return {
        type: 'MessageStatement',
        kind: token.type,
        value: token.value,
      }
    }
  },
  transform(node) {
    if (node.type === 'MessageStatement') {
      switch (node.kind) {
        case 'error':
          context.logger.error(node.value, { timestamp: true })
          break
        case 'warning':
          context.logger.warn(node.value, { timestamp: true })
          break
        case 'info':
          context.logger.info(node.value, { timestamp: true })
          break
      }
      return createProgramNode()
    }
  },
  generate(node, comment) {
    if (node.type === 'MessageStatement' && comment)
      return `${comment.start} #${node.kind} ${node.value} ${comment.end}`
  },
}))

enforce: 'pre' | 'post'

Execution priority of directives

• pre: Execute as early as possible
• post: Execute as late as possible