move regexp into constant

lib/single-file/single-file-core.js

@@ -1002,18 +1002,19 @@ this.SingleFileCore = this.SingleFileCore || (() => {
 				const resourceURL = DomUtil.normalizeURL(originalResourceURL);
 				if (resourceURL && resourceURL != baseURI && DomUtil.testValidPath(resourceURL) && stylesheetContent.includes(urlFunction)) {
 					const dataURI = await batchRequest.addURL(resourceURL);
+					const regExpUrlFunction = DomUtil.getRegExp(urlFunction);
 					if (!inline && options.compressCSS && dataURI.startsWith(PREFIX_DATA_URI_IMAGE) && !dataURI.startsWith(PREFIX_DATA_URI_IMAGE_SVG)) {
-						const functions = stylesheetContent.match(DomUtil.getRegExp(urlFunction));
+						const functions = stylesheetContent.match(regExpUrlFunction);
 						if (functions && functions.length > 1) {
 							const variableName = "--single-file-" + indexStyle + "-" + indexVariable;
 							stylesheetContent = variableName + ":url(\"" + dataURI + "\")" + (indexVariable ? ";" : "}") + stylesheetContent;
-							stylesheetContent = stylesheetContent.replace(DomUtil.getRegExp(urlFunction), "var(" + variableName + ")");
+							stylesheetContent = stylesheetContent.replace(regExpUrlFunction, "var(" + variableName + ")");
 							indexVariable++;
 						} else {
-							stylesheetContent = stylesheetContent.replace(DomUtil.getRegExp(urlFunction), urlFunction.replace(originalResourceURL, dataURI));
+							stylesheetContent = stylesheetContent.replace(regExpUrlFunction, urlFunction.replace(originalResourceURL, dataURI));
 						}
 					} else {
-						stylesheetContent = stylesheetContent.replace(DomUtil.getRegExp(urlFunction), urlFunction.replace(originalResourceURL, dataURI));
+						stylesheetContent = stylesheetContent.replace(regExpUrlFunction, urlFunction.replace(originalResourceURL, dataURI));
 					}
 				}
 			}));