webpack/lib/errors/LegacyJavascriptWarning.js

Packs ECMAScript/CommonJs/AMD modules for the browser. Allows you to split your codebase into multiple bundles, which can be loaded on demand. Supports loaders to preprocess files, i.e. json, jsx, es7, css, less, ... and your custom stuff.

/*
	MIT License http://www.opensource.org/licenses/mit-license.php
	Author Alexander Akait @alexander-akait
*/

"use strict";

const formatSize = require("../util/formatSize");
const WebpackError = require("./WebpackError");

/**
 * @typedef {object} LegacyPackageDetails
 * @property {string} name the package doing the emulating
 * @property {number} modules how many of its modules are in the build
 * @property {number} size bytes they contribute
 */

class LegacyJavascriptWarning extends WebpackError {
	/**
	 * Creates an instance of LegacyJavascriptWarning.
	 * @param {LegacyPackageDetails[]} packages the ones found, largest first
	 * @param {number} totalSize bytes they contribute between them
	 * @param {string[]} features the ones the target already has
	 */
	constructor(packages, totalSize, features) {
		const list = packages
			.map(
				(item) =>
					`\n  ${item.name} (${item.modules} ${
						item.modules === 1 ? "module" : "modules"
					}, ${formatSize(item.size)})`
			)
			.join("");

		super(
			`legacy javascript: ${formatSize(
				totalSize
			)} of the build emulates syntax the target already has natively:${list}\n'output.environment' says this target supports ${features.join(
				", "
			)}, so whatever lowers the syntax — usually '@babel/preset-env' — is compiling for older browsers than webpack is. Lining its targets up with the browserslist webpack reads drops them.\nFor more info visit https://webpack.js.org/configuration/target/#browserslist`
		);

		/** @type {string} */
		this.name = "LegacyJavascriptWarning";
	}
}

module.exports = LegacyJavascriptWarning;