enhanced-resolve/lib/AliasPlugin.js

/*
	MIT License http://www.opensource.org/licenses/mit-license.php
	Author Tobias Koppers @sokra
*/
"use strict";

function startsWith(string, searchString) {
	const stringLength = string.length;
	const searchLength = searchString.length;

	// early out if the search length is greater than the search string
	if(searchLength > stringLength) {
		return false;
	}
	let index = -1;
	while(++index < searchLength) {
		if(string.charCodeAt(index) !== searchString.charCodeAt(index)) {
			return false;
		}
	}
	return true;
}

module.exports = class AliasPlugin {
	constructor(source, options, target) {
		this.source = source;
		this.options = Array.isArray(options) ? options : [options];
		this.target = target;
	}

	apply(resolver) {
		const target = resolver.ensureHook(this.target);
		resolver.getHook(this.source).tapAsync("AliasPlugin", (request, resolveContext, callback) => {
			const innerRequest = request.request;
			if(!innerRequest) return callback();
			for(const item of this.options) {
				if(innerRequest === item.name || (!item.onlyModule && startsWith(innerRequest, item.name + "/"))) {
					if(innerRequest !== item.alias && !startsWith(innerRequest, item.alias + "/")) {
						const newRequestStr = item.alias + innerRequest.substr(item.name.length);
						const obj = Object.assign({}, request, {
							request: newRequestStr
						});
						return resolver.doResolve(target, obj, "aliased with mapping '" + item.name + "': '" + item.alias + "' to '" + newRequestStr + "'", resolveContext, (err, result) => {
							if(err) return callback(err);

							// Don't allow other aliasing or raw request
							if(result === undefined) return callback(null, null);
							callback(null, result);
						});
					}
				}
			}
			return callback();
		});
	}
};