webpack/lib/dependencies/HarmonyDetectionParserPlugin.js

Packs CommonJs/AMD modules for the browser. Allows to split your codebase into multiple bundles, which can be loaded on demand. Support 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 Tobias Koppers @sokra
*/

"use strict";

const DynamicExports = require("./DynamicExports");
const HarmonyCompatibilityDependency = require("./HarmonyCompatibilityDependency");
const HarmonyExports = require("./HarmonyExports");

module.exports = class HarmonyDetectionParserPlugin {
	constructor(options) {
		const { topLevelAwait = false } = options || {};
		this.topLevelAwait = topLevelAwait;
	}

	apply(parser) {
		parser.hooks.program.tap("HarmonyDetectionParserPlugin", ast => {
			const isStrictHarmony = parser.state.module.type === "javascript/esm";
			const isHarmony =
				isStrictHarmony ||
				ast.body.some(
					statement =>
						statement.type === "ImportDeclaration" ||
						statement.type === "ExportDefaultDeclaration" ||
						statement.type === "ExportNamedDeclaration" ||
						statement.type === "ExportAllDeclaration"
				);
			if (isHarmony) {
				const module = parser.state.module;
				const compatDep = new HarmonyCompatibilityDependency();
				compatDep.loc = {
					start: {
						line: -1,
						column: 0
					},
					end: {
						line: -1,
						column: 0
					},
					index: -3
				};
				module.addPresentationalDependency(compatDep);
				DynamicExports.bailout(parser.state);
				HarmonyExports.enable(parser.state, isStrictHarmony);
				parser.scope.isStrict = true;
			}
		});

		parser.hooks.topLevelAwait.tap("HarmonyDetectionParserPlugin", () => {
			const module = parser.state.module;
			if (!this.topLevelAwait) {
				throw new Error(
					"The top-level-await experiment is not enabled (set experiments.topLevelAwait: true to enabled it)"
				);
			}
			if (!HarmonyExports.isEnabled(parser.state)) {
				throw new Error(
					"Top-level-await is only supported in EcmaScript Modules"
				);
			}
			module.buildMeta.async = true;
		});

		const skipInHarmony = () => {
			if (HarmonyExports.isEnabled(parser.state)) {
				return true;
			}
		};

		const nullInHarmony = () => {
			if (HarmonyExports.isEnabled(parser.state)) {
				return null;
			}
		};

		const nonHarmonyIdentifiers = ["define", "exports"];
		for (const identifier of nonHarmonyIdentifiers) {
			parser.hooks.evaluateTypeof
				.for(identifier)
				.tap("HarmonyDetectionParserPlugin", nullInHarmony);
			parser.hooks.typeof
				.for(identifier)
				.tap("HarmonyDetectionParserPlugin", skipInHarmony);
			parser.hooks.evaluate
				.for(identifier)
				.tap("HarmonyDetectionParserPlugin", nullInHarmony);
			parser.hooks.expression
				.for(identifier)
				.tap("HarmonyDetectionParserPlugin", skipInHarmony);
			parser.hooks.call
				.for(identifier)
				.tap("HarmonyDetectionParserPlugin", skipInHarmony);
		}
	}
};