External Plugin

This is a third-party plugin. Please report issues in its Github Repository(opens new window)

hardhat(opens new window)

# hardhat-preprocessor

This plugin allows to pre-preocess contract source code before compilation

Hardhat(opens new window) preprocessor plugin.

# What

This plugin allow you to specify a function that is executed on every line of all contracts so that you can pre-process the code.

A typical example (included) is to remove console.log for production ready contracts.

Note that this plugin, by default, does not touch the filesystem. It happens in memory.

# Installation

npm install hardhat-preprocessor

And add the following statement to your hardhat.config.js:

import 'hardhat-preprocessor';

# Required plugins

Nothing required

# Tasks

hardhar-preprocessor also add a new task: preprocess

hardhat preprocess [--dest <destination folder>]

This task will write the modification to disk. By default it overwrite the sources. if the dest option is set, it will write in that folder instead (and keep sources intact).

# Environment extensions

No extra fields added to the envirobment.

# Configuration

This plugin extends the Hardhat Config with one new field: preprocess

This field is an object with a field : eachLine that itself is a function that accept the BRE as argument and must return either an object with a transform field or a promise to such object.

The transform function expect a string as argument (a line of a contract) and must return a string.

The object containing the transform function can also have a settings field that is used for caching. If no settings field is set, no caching will take place and contracts will be recompiled. If the settings field is set, then the contract will be recompiled only if the settings changed.

Note that instead of returning (or resolving a function), it is possible to return undefined to skip the preprocessing entirely. This will recompile contract if the previous invocation had returned something.

Basic example that add a comment on each line:

import 'hardhat-preprocessor';
export default {
  preprocess: {
    eachLine: (bre) => ({
      transform: (line) => line + '// comment at the end of each line',
      settings: {comment: true} // ensure the cache is working, in that example it can be anything as there is no option, the preprocessing happen all the time

The plugin comes also with a preprocess function to remove console.log (achieving the same thing as this plugin(opens new window) but without changing the files on disk)

You can use it as follow :

import {removeConsoleLog} from 'hardhat-preprocessor';
export default {
  preprocess: {
    eachLine: removeConsoleLog((bre) => bre.network.name !== 'hardhat' && bre.network.name !== 'localhost'),

In this example the preprocessing do not happen when used against hardhat (testing) or localhost

# Usage

There are no additional steps you need to take for this plugin to work.