improve performance of asNumber (#595)

Author: Uzlopak

lib/serializer.js

@@ -50,14 +50,17 @@ module.exports = class Serializer {
   }
 
   asNumber (i) {
-    const num = Number(i)
-    if (Number.isNaN(num)) {
+    if (typeof i !== 'number') {
+      i = Number(i)
+    }
+    // NaN !== NaN
+    if (i !== i) { // eslint-disable-line no-self-compare
       throw new Error(`The value "${i}" cannot be converted to a number.`)
-    } else if (!Number.isFinite(num)) {
-      return null
-    } else {
-      return '' + num
     }
+    if (i === Infinity || i === -Infinity) {
+      return 'null'
+    }
+    return '' + i
   }
 
   asBoolean (bool) {