fix: function asString argument types for trigger V8 optimization (monomorphi) (#689)

Author: nigrosimone

index.js

@@ -728,7 +728,21 @@ function buildSingleTypeSerializer (context, location, input) {
       } else if (schema.format === 'unsafe') {
         return `json += serializer.asUnsafeString(${input})`
       } else {
-        return `json += serializer.asString(${input})`
+        return `
+        if (typeof ${input} !== 'string') {
+          if (${input} === null) {
+            json += '""'
+          } else if (${input} instanceof Date) {
+            json += '"' + ${input}.toISOString() + '"'
+          } else if (${input} instanceof RegExp) {
+            json += serializer.asString(${input}.source)
+          } else {
+            json += serializer.asString(${input}.toString())
+          }
+        } else {
+          json += serializer.asString(${input})
+        }
+        `
       }
     }
     case 'integer':

lib/serializer.js

@@ -99,20 +99,6 @@ module.exports = class Serializer {
   }
 
   asString (str) {
-    if (typeof str !== 'string') {
-      if (str === null) {
-        return '""'
-      }
-      if (str instanceof Date) {
-        return '"' + str.toISOString() + '"'
-      }
-      if (str instanceof RegExp) {
-        str = str.source
-      } else {
-        str = str.toString()
-      }
-    }
-
     if (str.length < 42) {
       return this.asStringSmall(str)
     } else if (STR_ESCAPE.test(str) === false) {