webpack/lib/JavascriptGenerator.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 { RawSource, ReplaceSource } = require("webpack-sources");

// TODO: clean up this file
// replace with newer constructs

// TODO: remove DependencyVariables and replace them with something better

class JavascriptGenerator {
	generate(module, dependencyTemplates, runtimeTemplate) {
		const originalSource = module.originalSource();
		if (!originalSource) {
			return new RawSource("throw new Error('No source available');");
		}

		const source = new ReplaceSource(originalSource);

		this.sourceBlock(
			module,
			module,
			[],
			dependencyTemplates,
			source,
			runtimeTemplate
		);

		return source;
	}

	sourceBlock(
		module,
		block,
		availableVars,
		dependencyTemplates,
		source,
		runtimeTemplate
	) {
		for (const dependency of block.dependencies) {
			this.sourceDependency(
				dependency,
				dependencyTemplates,
				source,
				runtimeTemplate
			);
		}

		/**
		 * Get the variables of all blocks that we need to inject.
		 * These will contain the variable name and its expression.
		 * The name will be added as a parameter in a IIFE the expression as its value.
		 */
		const vars = block.variables.reduce((result, value) => {
			const variable = this.sourceVariables(
				value,
				availableVars,
				dependencyTemplates,
				runtimeTemplate
			);

			if (variable) {
				result.push(variable);
			}

			return result;
		}, []);

		/**
		 * if we actually have variables
		 * this is important as how #splitVariablesInUniqueNamedChunks works
		 * it will always return an array in an array which would lead to a IIFE wrapper around
		 * a module if we do this with an empty vars array.
		 */
		if (vars.length > 0) {
			/**
			 * Split all variables up into chunks of unique names.
			 * e.g. imagine you have the following variable names that need to be injected:
			 * [foo, bar, baz, foo, some, more]
			 * we can not inject "foo" twice, therefore we just make two IIFEs like so:
			 * (function(foo, bar, baz){
			 *   (function(foo, some, more){
			 *     …
			 *   }(…));
			 * }(…));
			 *
			 * "splitVariablesInUniqueNamedChunks" splits the variables shown above up to this:
			 * [[foo, bar, baz], [foo, some, more]]
			 */
			const injectionVariableChunks = this.splitVariablesInUniqueNamedChunks(
				vars
			);

			// create all the beginnings of IIFEs
			const functionWrapperStarts = injectionVariableChunks.map(
				variableChunk => {
					return this.variableInjectionFunctionWrapperStartCode(
						variableChunk.map(variable => variable.name)
					);
				}
			);

			// and all the ends
			const functionWrapperEnds = injectionVariableChunks.map(variableChunk => {
				return this.variableInjectionFunctionWrapperEndCode(
					module,
					variableChunk.map(variable => variable.expression),
					block
				);
			});

			// join them to one big string
			const varStartCode = functionWrapperStarts.join("");

			// reverse the ends first before joining them, as the last added must be the inner most
			const varEndCode = functionWrapperEnds.reverse().join("");

			// if we have anything, add it to the source
			if (varStartCode && varEndCode) {
				const start = block.range ? block.range[0] : -10;
				const end = block.range
					? block.range[1]
					: module.originalSource().size() + 1;
				source.insert(start + 0.5, varStartCode);
				source.insert(end + 0.5, "\n/* WEBPACK VAR INJECTION */" + varEndCode);
			}
		}

		for (const childBlock of block.blocks) {
			this.sourceBlock(
				module,
				childBlock,
				availableVars.concat(vars),
				dependencyTemplates,
				source,
				runtimeTemplate
			);
		}
	}

	sourceDependency(dependency, dependencyTemplates, source, runtimeTemplate) {
		const template = dependencyTemplates.get(dependency.constructor);
		if (!template) {
			throw new Error(
				"No template for dependency: " + dependency.constructor.name
			);
		}
		template.apply(dependency, source, runtimeTemplate, dependencyTemplates);
	}

	sourceVariables(
		variable,
		availableVars,
		dependencyTemplates,
		runtimeTemplate
	) {
		const name = variable.name;
		const expr = variable.expressionSource(
			dependencyTemplates,
			runtimeTemplate
		);

		if (
			availableVars.some(
				v => v.name === name && v.expression.source() === expr.source()
			)
		) {
			return;
		}
		return {
			name: name,
			expression: expr
		};
	}

	/*
	 * creates the start part of a IIFE around the module to inject a variable name
	 * (function(…){   <- this part
	 * }.call(…))
	 */
	variableInjectionFunctionWrapperStartCode(varNames) {
		const args = varNames.join(", ");
		return `/* WEBPACK VAR INJECTION */(function(${args}) {`;
	}

	contextArgument(module, block) {
		if (this === block) {
			return module.exportsArgument;
		}
		return "this";
	}

	/*
	 * creates the end part of a IIFE around the module to inject a variable name
	 * (function(…){
	 * }.call(…))   <- this part
	 */
	variableInjectionFunctionWrapperEndCode(module, varExpressions, block) {
		const firstParam = this.contextArgument(module, block);
		const furtherParams = varExpressions.map(e => e.source()).join(", ");
		return `}.call(${firstParam}, ${furtherParams}))`;
	}

	splitVariablesInUniqueNamedChunks(vars) {
		const startState = [[]];
		return vars.reduce((chunks, variable) => {
			const current = chunks[chunks.length - 1];
			// check if variable with same name exists already
			// if so create a new chunk of variables.
			const variableNameAlreadyExists = current.some(
				v => v.name === variable.name
			);

			if (variableNameAlreadyExists) {
				// start new chunk with current variable
				chunks.push([variable]);
			} else {
				// else add it to current chunk
				current.push(variable);
			}
			return chunks;
		}, startState);
	}
}

module.exports = JavascriptGenerator;