webpack/lib/dependencies/HarmonyExportInitFragment.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 InitFragment = require("../InitFragment");
const RuntimeGlobals = require("../RuntimeGlobals");

/** @typedef {import("webpack-sources").Source} Source */
/** @typedef {import("../Generator").GenerateContext} GenerateContext */

const joinIterableWithComma = iterable => {
	// This is more performant than Array.from().join(", ")
	// as it doesn't create an array
	let str = "";
	let first = true;
	for (const item of iterable) {
		if (first) {
			first = false;
		} else {
			str += ", ";
		}
		str += item;
	}
	return str;
};

const EMPTY_MAP = new Map();
const EMPTY_SET = new Set();

class HarmonyExportInitFragment extends InitFragment {
	/**
	 * @param {string} exportsArgument the exports identifier
	 * @param {Map<string, string>} exportMap mapping from used name to exposed variable name
	 * @param {Set<string>} unusedExports list of unused export names
	 */
	constructor(
		exportsArgument,
		exportMap = EMPTY_MAP,
		unusedExports = EMPTY_SET
	) {
		super(undefined, InitFragment.STAGE_HARMONY_EXPORTS, 1, "harmony-exports");
		this.exportsArgument = exportsArgument;
		this.exportMap = exportMap;
		this.unusedExports = unusedExports;
	}

	merge(other) {
		let exportMap;
		if (this.exportMap.size === 0) {
			exportMap = other.exportMap;
		} else if (other.exportMap.size === 0) {
			exportMap = this.exportMap;
		} else {
			exportMap = new Map(other.exportMap);
			for (const [key, value] of this.exportMap) {
				if (!exportMap.has(key)) exportMap.set(key, value);
			}
		}
		let unusedExports;
		if (this.unusedExports.size === 0) {
			unusedExports = other.unusedExports;
		} else if (other.unusedExports.size === 0) {
			unusedExports = this.unusedExports;
		} else {
			unusedExports = new Set(other.unusedExports);
			for (const value of this.unusedExports) {
				unusedExports.add(value);
			}
		}
		return new HarmonyExportInitFragment(
			this.exportsArgument,
			exportMap,
			unusedExports
		);
	}

	/**
	 * @param {GenerateContext} generateContext context for generate
	 * @returns {string|Source} the source code that will be included as initialization code
	 */
	getContent({ runtimeTemplate, runtimeRequirements }) {
		runtimeRequirements.add(RuntimeGlobals.exports);
		runtimeRequirements.add(RuntimeGlobals.definePropertyGetters);

		const unusedPart =
			this.unusedExports.size > 1
				? `/* unused harmony exports ${joinIterableWithComma(
						this.unusedExports
				  )} */\n`
				: this.unusedExports.size > 0
				? `/* unused harmony export ${
						this.unusedExports.values().next().value
				  } */\n`
				: "";
		const definitions = [];
		for (const [key, value] of this.exportMap) {
			definitions.push(
				`\n/* harmony export */   ${JSON.stringify(
					key
				)}: ${runtimeTemplate.returningFunction(value)}`
			);
		}
		const definePart =
			this.exportMap.size > 0
				? `/* harmony export */ ${RuntimeGlobals.definePropertyGetters}(${
						this.exportsArgument
				  }, {${definitions.join(",")}\n/* harmony export */ });\n`
				: "";
		return `${definePart}${unusedPart}`;
	}
}

module.exports = HarmonyExportInitFragment;