Optimize N-Quads escape replacement.

- Use a pre-computed map of replacement values.
- Performance difference depends on the number of replacements. The
  rdf-canon escaping test showed up to 15% improvement.

CHANGELOG.md

@@ -34,10 +34,14 @@
   - Node.js using the improved browser algorithm can be ~4-9% faster overall.
   - Node.js native `Buffer` conversion can be ~5-12% faster overall.
 - Optimize a N-Quads serialization call.
-- Optimize N-Quads escape/unescape:
+- Optimize N-Quads escape/unescape calling replace:
   - Run regex test before doing a replace call.
   - Performance difference depends on data and how often escape/unescape would
     need to be called. A benchmark test data showed ~3-5% overall improvement.
+- Optimize N-Quads escape replacement:
+  - Use a pre-computed map of replacement values.
+  - Performance difference depends on the number of replacements. The
+    [rdf-canon][] escaping test showed up to 15% improvement.
 
 ### Fixed
 - Disable native lib tests in a browser.

lib/NQuads.js

@@ -382,6 +382,25 @@ function _compareTriples(t1, t2) {
 }
 
 const _stringLiteralEscapeRegex = /[\u0000-\u001F\u007F"\\]/g;
+const _stringLiteralEscapeMap = [];
+for(let n = 0; n <= 0x7f; ++n) {
+  if(_stringLiteralEscapeRegex.test(String.fromCharCode(n))) {
+    // default UCHAR mapping
+    _stringLiteralEscapeMap[n] =
+      '\\u' + n.toString(16).toUpperCase().padStart(4, '0');
+    // reset regex
+    _stringLiteralEscapeRegex.lastIndex = 0;
+  }
+}
+// special ECHAR mappings
+_stringLiteralEscapeMap['\b'.codePointAt(0)] = '\\b';
+_stringLiteralEscapeMap['\t'.codePointAt(0)] = '\\t';
+_stringLiteralEscapeMap['\n'.codePointAt(0)] = '\\n';
+_stringLiteralEscapeMap['\f'.codePointAt(0)] = '\\f';
+_stringLiteralEscapeMap['\r'.codePointAt(0)] = '\\r';
+_stringLiteralEscapeMap['"' .codePointAt(0)] = '\\"';
+_stringLiteralEscapeMap['\\'.codePointAt(0)] = '\\\\';
+
 /**
  * Escape string to N-Quads literal
  */
@@ -390,26 +409,13 @@ function _stringLiteralEscape(s) {
     return s;
   }
   return s.replace(_stringLiteralEscapeRegex, function(match) {
-    switch(match) {
-      case '\b': return '\\b';
-      case '\t': return '\\t';
-      case '\n': return '\\n';
-      case '\f': return '\\f';
-      case '\r': return '\\r';
-      case '"': return '\\"';
-      case '\\': return '\\\\';
-      case '\u007F': return '\\u007F';
-    }
-    return '\\u' + match
-      .codePointAt(0)
-      .toString(16)
-      .toUpperCase()
-      .padStart(4, '0');
+    return _stringLiteralEscapeMap[match.codePointAt(0)];
   });
 }
 
 const _stringLiteralUnescapeRegex =
   /(?:\\([btnfr"'\\]))|(?:\\u([0-9A-Fa-f]{4}))|(?:\\U([0-9A-Fa-f]{8}))/g;
+
 /**
  * Unescape N-Quads literal to string
  */
@@ -440,6 +446,17 @@ function _stringLiteralUnescape(s) {
 }
 
 const _iriEscapeRegex = /[\u0000-\u0020<>"{}|^`\\]/g;
+const _iriEscapeRegexMap = [];
+for(let n = 0; n <= 0x7f; ++n) {
+  if(_iriEscapeRegex.test(String.fromCharCode(n))) {
+    // UCHAR mapping
+    _iriEscapeRegexMap[n] =
+      '\\u' + n.toString(16).toUpperCase().padStart(4, '0');
+    // reset regex
+    _iriEscapeRegex.lastIndex = 0;
+  }
+}
+
 /**
  * Escape IRI to N-Quads IRI
  */
@@ -448,12 +465,13 @@ function _iriEscape(s) {
     return s;
   }
   return s.replace(_iriEscapeRegex, function(match) {
-    return '\\u' + match.codePointAt(0).toString(16).padStart(4, '0');
+    return _iriEscapeRegexMap[match.codePointAt(0)];
   });
 }
 
 const _iriUnescapeRegex =
   /(?:\\u([0-9A-Fa-f]{4}))|(?:\\U([0-9A-Fa-f]{8}))/g;
+
 /**
  * Unescape N-Quads IRI to IRI
  */