performance improvement

- replace substr with direct char code comparison
- improve tagExpWithClosingIndex

Author: amitguptagwl

src/xmlparser/OrderedObjParser.js

@@ -310,7 +310,8 @@ const parseXml = function (xmlData) {
     if (ch === '<') {
       // const nextIndex = i+1;
       // const _2ndChar = xmlData[nextIndex];
-      if (xmlData[i + 1] === '/') {//Closing Tag
+      const c1 = xmlData.charCodeAt(i + 1);
+      if (c1 === 47) {//Closing Tag '/'
         const closeIndex = findClosingIndex(xmlData, ">", i, "Closing Tag is not closed.")
         let tagName = xmlData.substring(i + 2, closeIndex).trim();
 
@@ -344,7 +345,7 @@ const parseXml = function (xmlData) {
         currentNode = this.tagsNodeStack.pop();//avoid recursion, set the parent tag scope
         textData = "";
         i = closeIndex;
-      } else if (xmlData[i + 1] === '?') {
+      } else if (c1 === 63) { //'?'
 
         let tagData = readTagExp(xmlData, i, false, "?>");
         if (!tagData) throw new Error("Pi Tag is not closed.");
@@ -365,7 +366,9 @@ const parseXml = function (xmlData) {
 
 
         i = tagData.closeIndex + 1;
-      } else if (xmlData.substr(i + 1, 3) === '!--') {
+      } else if (c1 === 33
+        && xmlData.charCodeAt(i + 2) === 45
+        && xmlData.charCodeAt(i + 3) === 45) { //'!--'
         const endIndex = findClosingIndex(xmlData, "-->", i + 4, "Comment is not closed.")
         if (this.options.commentPropName) {
           const comment = xmlData.substring(i + 4, endIndex - 2);
@@ -375,11 +378,13 @@ const parseXml = function (xmlData) {
           currentNode.add(this.options.commentPropName, [{ [this.options.textNodeName]: comment }]);
         }
         i = endIndex;
-      } else if (xmlData.substr(i + 1, 2) === '!D') {
+      } else if (c1 === 33
+        && xmlData.charCodeAt(i + 2) === 68) { //'!D'
         const result = docTypeReader.readDocType(xmlData, i);
         this.docTypeEntities = result.entities;
         i = result.i;
-      } else if (xmlData.substr(i + 1, 2) === '![') {
+      } else if (c1 === 33
+        && xmlData.charCodeAt(i + 2) === 91) { // '!['
         const closeIndex = findClosingIndex(xmlData, "]]>", i, "CDATA is not closed.") - 2;
         const tagExp = xmlData.substring(i + 9, closeIndex);
 
@@ -735,32 +740,33 @@ function isItStopNode(stopNodeExpressions, matcher) {
  * @returns 
  */
 function tagExpWithClosingIndex(xmlData, i, closingChar = ">") {
-  let attrBoundary;
-  let tagExp = "";
-  for (let index = i; index < xmlData.length; index++) {
-    let ch = xmlData[index];
+  let attrBoundary = 0;
+  const chars = [];
+  const len = xmlData.length;
+  const closeCode0 = closingChar.charCodeAt(0);
+  const closeCode1 = closingChar.length > 1 ? closingChar.charCodeAt(1) : -1;
+
+  for (let index = i; index < len; index++) {
+    const code = xmlData.charCodeAt(index);
+
     if (attrBoundary) {
-      if (ch === attrBoundary) attrBoundary = "";//reset
-    } else if (ch === '"' || ch === "'") {
-      attrBoundary = ch;
-    } else if (ch === closingChar[0]) {
-      if (closingChar[1]) {
-        if (xmlData[index + 1] === closingChar[1]) {
-          return {
-            data: tagExp,
-            index: index
-          }
+      if (code === attrBoundary) attrBoundary = 0;
+    } else if (code === 34 || code === 39) { // " or '
+      attrBoundary = code;
+    } else if (code === closeCode0) {
+      if (closeCode1 !== -1) {
+        if (xmlData.charCodeAt(index + 1) === closeCode1) {
+          return { data: String.fromCharCode(...chars), index };
         }
       } else {
-        return {
-          data: tagExp,
-          index: index
-        }
+        return { data: String.fromCharCode(...chars), index };
       }
-    } else if (ch === '\t') {
-      ch = " "
+    } else if (code === 9) { // \t
+      chars.push(32); // space
+      continue;
     }
-    tagExp += ch;
+
+    chars.push(code);
   }
 }
 
@@ -816,7 +822,8 @@ function readStopNodeData(xmlData, tagName, i) {
 
   for (; i < xmlData.length; i++) {
     if (xmlData[i] === "<") {
-      if (xmlData[i + 1] === "/") {//close tag
+      const c1 = xmlData.charCodeAt(i + 1);
+      if (c1 === 47) {//close tag '/'
         const closeIndex = findClosingIndex(xmlData, ">", i, `${tagName} is not closed`);
         let closeTagName = xmlData.substring(i + 2, closeIndex).trim();
         if (closeTagName === tagName) {
@@ -829,13 +836,16 @@ function readStopNodeData(xmlData, tagName, i) {
           }
         }
         i = closeIndex;
-      } else if (xmlData[i + 1] === '?') {
+      } else if (c1 === 63) { //?
         const closeIndex = findClosingIndex(xmlData, "?>", i + 1, "StopNode is not closed.")
         i = closeIndex;
-      } else if (xmlData.substr(i + 1, 3) === '!--') {
+      } else if (c1 === 33
+        && xmlData.charCodeAt(i + 2) === 45
+        && xmlData.charCodeAt(i + 3) === 45) { // '!--'
         const closeIndex = findClosingIndex(xmlData, "-->", i + 3, "StopNode is not closed.")
         i = closeIndex;
-      } else if (xmlData.substr(i + 1, 2) === '![') {
+      } else if (c1 === 33
+        && xmlData.charCodeAt(i + 2) === 91) { // '!['
         const closeIndex = findClosingIndex(xmlData, "]]>", i, "StopNode is not closed.") - 2;
         i = closeIndex;
       } else {