use hasOwnProperty from prototype (#510)

Author: Uzlopak

index.js

@@ -346,12 +346,12 @@ function buildCode (location) {
       schema.properties[key] = propertyLocation.schema
     }
 
-    // Using obj['key'] !== undefined instead of obj.hasOwnProperty(prop) for perf reasons,
-    // see https://github.com/mcollina/fast-json-stringify/pull/3 for discussion.
-
     const sanitized = JSON.stringify(key)
     const asString = JSON.stringify(sanitized)
 
+    // Using obj['key'] !== undefined instead of obj.hasOwnProperty(prop) for perf reasons,
+    // see https://github.com/mcollina/fast-json-stringify/pull/3 for discussion.
+
     code += `
       if (obj[${sanitized}] !== undefined) {
         ${addComma}
@@ -901,7 +901,7 @@ function buildValue (location, input) {
           switch (type) {
             case 'string': {
               code += `
-                ${statement}(${input} === null || typeof ${input} === "${type}" || ${input} instanceof RegExp || (typeof ${input} === "object" && Object.hasOwnProperty.call(${input}, "toString")))
+                ${statement}(${input} === null || typeof ${input} === "${type}" || ${input} instanceof RegExp || (typeof ${input} === "object" && Object.prototype.hasOwnProperty.call(${input}, "toString")))
                   ${nestedResult}
               `
               break
@@ -987,7 +987,7 @@ function extendDateTimeType (schema) {
 function isEmpty (schema) {
   // eslint-disable-next-line
   for (var key in schema) {
-    if (schema.hasOwnProperty(key) && schema[key] !== undefined) {
+    if (Object.prototype.hasOwnProperty.call(schema, key) && schema[key] !== undefined) {
       return false
     }
   }