improve performance of asInteger serializer (#589)

Author: Uzlopak

lib/serializer.js

@@ -23,17 +23,28 @@ module.exports = class Serializer {
   }
 
   asInteger (i) {
-    if (typeof i === 'bigint') {
+    if (typeof i === 'number') {
+      if (i === Infinity || i === -Infinity) {
+        throw new Error(`The value "${i}" cannot be converted to an integer.`)
+      }
+      if ((i | 0) === i) {
+        return '' + i
+      }
+      if (Number.isNaN(i)) {
+        throw new Error(`The value "${i}" cannot be converted to an integer.`)
+      }
+      return this.parseInteger(i)
+    } else if (i === null) {
+      return '0'
+    } else if (typeof i === 'bigint') {
       return i.toString()
-    } else if (Number.isInteger(i)) {
-      return '' + i
     } else {
       /* eslint no-undef: "off" */
       const integer = this.parseInteger(i)
-      if (Number.isNaN(integer) || !Number.isFinite(integer)) {
-        throw new Error(`The value "${i}" cannot be converted to an integer.`)
-      } else {
+      if (Number.isFinite(integer)) {
         return '' + integer
+      } else {
+        throw new Error(`The value "${i}" cannot be converted to an integer.`)
       }
     }
   }