index.js

/**
 * @author Kir_Antipov
 * See LICENSE.md file in root directory for full license.
 */

"use strict";

const { Buffer } = require("buffer");
const path = require("path");
const webpack = require("webpack");
const version = +webpack.version.split(".")[0];
// Webpack 5 exposes the sources property to ensure the right version of webpack-sources is used.
// require('webpack-sources') approach may result in the "Cannot find module 'webpack-sources'" error.
const { Source, RawSource } = webpack.sources || require("webpack-sources");

/**
 * @typedef {object} EmitFilePluginOptions
 *
 * @property {string} path
 * OPTIONAL: defaults to the Webpack output path.
 * Output path.
 * Can be relative (to Webpack output path) or absolute.
 *
 * @property {string} filename
 * REQUIRED.
 * Name of the file to add to assets.
 *
 * @property {number} stage
 * OPTIONAL: defaults to the webpack.Compilation.PROCESS_ASSETS_STAGE_ADDITIONAL.
 * Asset processing stage.
 *
 * @property {string|Buffer|Source|((assets: Record<string, Source>) => (string|Buffer|Source))|((assets: Record<string, Source>) => (Promise<string|Buffer|Source>))} content
 * REQUIRED.
 * File content. Can be either a string, a buffer, or a (asynchronous) function.
 * If the resulting object is not a string or a buffer, it will be converted to JSON.
 */

/**
 * Webpack plugin to emit files.
 *
 * @param {EmitFilePluginOptions} options The EmitFilePlugin config.
 */
function EmitFilePlugin(options) {
    if (!options) {
        throw new Error(`${EmitFilePlugin.name}: Please provide 'options' for the ${EmitFilePlugin.name} config.`);
    }

    if (!options.filename) {
        throw new Error(`${EmitFilePlugin.name}: Please provide 'options.filename' in the ${EmitFilePlugin.name} config.`);
    }

    if (!options.content && options.content !== "") {
        throw new Error(`${EmitFilePlugin.name}: Please provide 'options.content' in the ${EmitFilePlugin.name} config.`);
    }

    if (typeof options.stage == "number" && version < 5) {
        console.warn(`${EmitFilePlugin.name}: 'options.stage' is only available for Webpack version 5 and higher.`);
    }

    this.options = options;
}

/**
 * Plugin entry point.
 *
 * @param {webpack.Compiler} compiler The compiler.
 */
EmitFilePlugin.prototype.apply = function (compiler) {
    if (version < 4) {
        compiler.plugin("emit", (compilation, callback) => emitFile(this.options, compilation, callback, callback));
    } else if (version == 4) {
        compiler.hooks.emit.tapAsync(EmitFilePlugin.name, (compilation, callback) => emitFile(this.options, compilation, callback, callback));
    } else {
        compiler.hooks.thisCompilation.tap(EmitFilePlugin.name, compilation => {
            compilation.hooks.processAssets.tapPromise(
                {
                    name: EmitFilePlugin.name,
                    stage: typeof this.options.stage == "number" ? this.options.stage : webpack.Compilation.PROCESS_ASSETS_STAGE_ADDITIONAL,
                },
                () => new Promise((resolve, reject) => emitFile(this.options, compilation, resolve, reject))
            );
        });
    }
};

/**
 * @param {EmitFilePluginOptions} options
 * @param {webpack.Compilation} compilation
 * @param {() => void} resolve
 */
function emitFile(options, compilation, resolve) {
    const outputPath = options.path || compilation.options.output.path;

    let filename = options.filename;

    if (options.hash) {
      if (options.filename.includes('[hash]')) {
        filename = options.filename.replace('[hash]', compilation.hash);
      } else {
        filename = `${options.filename}?${compilation.hash}`;
      }
    }

    const outputPathAndFilename = path.resolve(
        compilation.options.output.path,
        outputPath,
        filename
    );

    const relativeOutputPath = path.relative(
        compilation.options.output.path,
        outputPathAndFilename
    );

    const contentOrPromise = typeof options.content == "function"
        ? options.content(compilation.assets)
        : options.content;

    const contentPromise = contentOrPromise instanceof Promise
        ? contentOrPromise
        : new Promise(resolve => resolve(contentOrPromise));

    contentPromise.then(content => {
        const source = content instanceof Source
            ? content
            : new RawSource((typeof content == "string" || content instanceof Buffer) ? content : JSON.stringify(content));

        if (version < 5) {
            compilation.assets[relativeOutputPath] = source;
        } else {
            compilation.emitAsset(relativeOutputPath, source);
        }

        resolve();
    });
}

module.exports = EmitFilePlugin;