refactor source method of ExternalModule

lib/ExternalModule.js

@@ -37,52 +37,74 @@ class ExternalModule extends Module {
 		callback();
 	}
 
-	source() {
-		let str = "throw new Error('Externals not supported');";
-		let request = this.request;
-		if(typeof request === "object") request = request[this.type];
+	getSourceForGlobalVariableExternal(request, type) {
+		if(!Array.isArray(request)) {
+			return `(function() { module.exports = ${type}[${JSON.stringify(request)}]; }());`;
+		}
+
+		// needed for e.g. window["some"]["thing"]
+		const objectLookup = request.map(r => `[${JSON.stringify(r)}]`).join("");
+		return `(function() { module.exports = ${type}${objectLookup}; }());`;
+	}
+
+	getSourceForCommonJsExternal(request) {
+		if(!Array.isArray(request)) {
+			return `module.exports = require(${JSON.stringify(request)});`;
+		}
+
+		const moduleName = request[0];
+		const objectLookup = request.slice(1).map(r => `[${JSON.stringify(r)}]`).join("");
+		return `module.exports = require(${moduleName})${objectLookup};`;
+	}
+
+	checkExternalVariable(variableToCheck, request) {
+		return `if(typeof ${variableToCheck} === 'undefined') {${WebpackMissingModule.moduleCode(request)}}`;
+	}
+
+	getSourceForAmdOrUmdExternal(request, id, optional) {
+		const externalVariable = `__WEBPACK_EXTERNAL_MODULE_${id}__`;
+		const missingModuleError = optional ? this.checkExternalVariable(externalVariable, request) : "";
+		return `${missingModuleError}
+module.exports = ${externalVariable};`;
+	}
+
+	getSourceForDefaultCase(request, optional) {
+		const missingModuleError = optional ? this.checkExternalVariable(request, request) : "";
+		return `${missingModuleError}
+module.exports = ${request};`;
+	}
+
+	getSourceString() {
+		const request = typeof this.request === "object" ? this.request[this.type] : this.request;
 		switch(this.type) {
 			case "this":
 			case "window":
 			case "global":
-				if(Array.isArray(request)) {
-					str = "(function() { module.exports = " + this.type + request.map(function(r) {
-						return "[" + JSON.stringify(r) + "]";
-					}).join("") + "; }());";
-				} else
-					str = "(function() { module.exports = " + this.type + "[" + JSON.stringify(request) + "]; }());";
-				break;
+				return this.getSourceForGlobalVariableExternal(request, this.type);
 			case "commonjs":
 			case "commonjs2":
-				if(Array.isArray(request)) {
-					str = "module.exports = require(" + JSON.stringify(request[0]) + ")" + request.slice(1).map(function(r) {
-						return "[" + JSON.stringify(r) + "]";
-					}).join("") + ";";
-				} else
-					str = "module.exports = require(" + JSON.stringify(request) + ");";
-				break;
+				return this.getSourceForCommonJsExternal(request);
 			case "amd":
 			case "umd":
 			case "umd2":
-				str = "";
-				if(this.optional) {
-					str += "if(typeof __WEBPACK_EXTERNAL_MODULE_" + this.id + "__ === 'undefined') {" + WebpackMissingModule.moduleCode(request) + "}\n";
-				}
-				str += "module.exports = __WEBPACK_EXTERNAL_MODULE_" + this.id + "__;";
-				break;
+				return this.getSourceForAmdOrUmdExternal(request, this.id, this.optional);
 			default:
-				str = "";
-				if(this.optional) {
-					str += "if(typeof " + request + " === 'undefined') {" + WebpackMissingModule.moduleCode(request) + "}\n";
-				}
-				str += "module.exports = " + request + ";";
-				break;
+				return this.getSourceForDefaultCase(request, this.optional);
 		}
+	}
+
+	getSource(sourceString) {
 		if(this.useSourceMap) {
-			return new OriginalSource(str, this.identifier());
-		} else {
-			return new RawSource(str);
+			return new OriginalSource(sourceString, this.identifier());
 		}
+
+		return new RawSource(sourceString);
+	}
+
+	source() {
+		return this.getSource(
+			this.getSourceString()
+		);
 	}
 
 	size() {