avoid main encapsulation for simple object (#594)

* avoid main encapsulation for simple object

* avoid ternary operation and add a comment

Author: Uzlopak

benchmark/bench.js

@@ -214,6 +214,27 @@ const benchmarks = [
       b5: true
     }
   },
+  {
+    name: 'simple object',
+    schema: {
+      title: 'Example Schema',
+      type: 'object',
+      properties: {
+        firstName: {
+          type: 'string'
+        },
+        lastName: {
+          type: ['string', 'null']
+        },
+        age: {
+          description: 'Age in years',
+          type: 'integer',
+          minimum: 0
+        }
+      }
+    },
+    input: { firstName: 'Max', lastName: 'Power', age: 22 }
+  },
   {
     name: 'object with const string property',
     schema: {

index.js

@@ -123,15 +123,30 @@ function build (schema, options) {
   const location = new Location(schema, rootSchemaId)
   const code = buildValue(location, 'input')
 
-  const contextFunctionCode = `
+  let contextFunctionCode
+
+  // If we have only the invocation of the 'anonymous0' function, we would
+  // basically just wrap the 'anonymous0' function in the 'main' function and
+  // and the overhead of the intermediate variabe 'json'. We can avoid the
+  // wrapping and the unnecessary memory allocation by aliasing 'anonymous0' to
+  // 'main'
+  if (code === 'json += anonymous0(input)') {
+    contextFunctionCode = `
+    ${contextFunctions.join('\n')}
+    const main = anonymous0
+    return main
+    `
+  } else {
+    contextFunctionCode = `
     function main (input) {
       let json = ''
       ${code}
       return json
     }
     ${contextFunctions.join('\n')}
     return main
-  `
+    `
+  }
 
   const serializer = new Serializer(options)
   const validator = new Validator(options.ajv)