Minor performance improvements

Author: matt-aitken

apps/webapp/app/utils/detectBadJsonStrings.ts

@@ -3,19 +3,30 @@ export function detectBadJsonStrings(jsonString: string): boolean {
   let idx = jsonString.indexOf("\\u");
   if (idx === -1) return false;
 
-  // Only check the area around each \u
-  while (idx !== -1 && idx < jsonString.length - 5) {
+  // Use a more efficient scanning strategy
+  const length = jsonString.length;
+
+  while (idx !== -1 && idx < length - 5) {
+    // Only check if we have enough characters left
+    if (idx + 6 > length) break;
+
     if (jsonString[idx + 1] === "u" && jsonString[idx + 2] === "d") {
       const third = jsonString[idx + 3];
-      // High surrogate
+
+      // High surrogate check
       if (
         /[89ab]/.test(third) &&
         /[0-9a-f]/.test(jsonString[idx + 4]) &&
         /[0-9a-f]/.test(jsonString[idx + 5])
       ) {
-        // Check for low surrogate after
+        // Check for low surrogate after (need at least 6 more chars)
+        if (idx + 12 > length) {
+          return true; // Incomplete high surrogate (not enough chars left)
+        }
+
         if (
-          jsonString.substr(idx + 6, 2) !== "\\u" ||
+          jsonString[idx + 6] !== "\\" ||
+          jsonString[idx + 7] !== "u" ||
           jsonString[idx + 8] !== "d" ||
           !/[cd]/.test(jsonString[idx + 9]) ||
           !/[0-9a-f]/.test(jsonString[idx + 10]) ||
@@ -24,16 +35,21 @@ export function detectBadJsonStrings(jsonString: string): boolean {
           return true; // Incomplete high surrogate
         }
       }
-      // Low surrogate
+
+      // Low surrogate check
       if (
         (third === "c" || third === "d") &&
         /[0-9a-f]/.test(jsonString[idx + 4]) &&
         /[0-9a-f]/.test(jsonString[idx + 5])
       ) {
-        // Check for high surrogate before
+        // Check for high surrogate before (need at least 6 chars before)
+        if (idx < 6) {
+          return true; // Incomplete low surrogate (not enough chars before)
+        }
+
         if (
-          idx < 6 ||
-          jsonString.substr(idx - 6, 2) !== "\\u" ||
+          jsonString[idx - 6] !== "\\" ||
+          jsonString[idx - 5] !== "u" ||
           jsonString[idx - 4] !== "d" ||
           !/[89ab]/.test(jsonString[idx - 3]) ||
           !/[0-9a-f]/.test(jsonString[idx - 2]) ||
@@ -43,7 +59,10 @@ export function detectBadJsonStrings(jsonString: string): boolean {
         }
       }
     }
-    idx = jsonString.indexOf("\\u", idx + 1);
+
+    // More efficient next search - skip ahead by 2 to avoid overlapping matches
+    idx = jsonString.indexOf("\\u", idx + 2);
   }
+
   return false;
 }

apps/webapp/test/detectbadJsonStrings.test.ts

@@ -172,6 +172,13 @@ describe("detectBadJsonStrings", () => {
         2
       )}x slower for Unicode strings`
     );
+
+    // Both cases should be extremely fast (under 1 microsecond per call)
+    expect(noUnicodeTime / iterations).toBeLessThan(0.001); // Less than 1 microsecond
+    expect(withUnicodeTime / iterations).toBeLessThan(0.001); // Less than 1 microsecond
+
+    // The difference should be reasonable (not more than 5x)
+    expect(noUnicodeTime / withUnicodeTime).toBeLessThan(5);
   });
 });