Converts _createWriter in RecordType prototype chain

lib/types.js

@@ -2300,33 +2300,37 @@ RecordType.prototype._createSkipper = function () {
 RecordType.prototype._createWriter = function () {
   // jshint -W054
   // We still do default handling here, in case a normal JS object is passed.
-  var args = [];
-  var name = this._getConstructorName();
-  var body = 'return function write' + name + '(t, v) {\n';
+
   var values = [];
-  var i, l, field, value;
-  for (i = 0, l = this.fields.length; i < l; i++) {
-    field = this.fields[i];
-    args.push('t' + i);
+  var dValues = {};
+  this.fields.forEach((field, i) => {
     values.push(field.type);
-    body += '  ';
-    if (field.defaultValue() === undefined) {
-      body += 't' + i + '._write(t, v.' + field.name + ');\n';
-    } else {
-      value = field.type.toBuffer(field.defaultValue()).toString('binary');
-      // Convert the default value to a binary string ahead of time. We aren't
-      // converting it to a buffer to avoid retaining too much memory. If we
-      // had our own buffer pool, this could be an idea in the future.
-      args.push('d' + i);
-      values.push(value);
-      body += 'var v' + i + ' = v.' + field.name + ';\n';
-      body += 'if (v' + i + ' === undefined) {\n';
-      body += '    t.writeBinary(d' + i + ', ' + value.length + ');\n';
-      body += '  } else {\n    t' + i + '._write(t, v' + i + ');\n  }\n';
-    }
-  }
-  body += '}';
-  return new Function(args.join(), body).apply(undefined, values);
+    if (field.defaultValue() !== undefined) {
+      dValues[i] = field.type.toBuffer(field.defaultValue()).toString('binary');
+    }
+  });
+  var self = this;
+  function ConstructorFunction(vv, dv) {
+    var constructorName = self._getConstructorName();
+    var innerFunction = ({
+      [constructorName]: function (t, v) {
+        for (var i=0, l = self.fields.length; i<l; i++) {
+          let f = self.fields[i];
+          if (f.defaultValue() === undefined) {
+            vv[i]._write(t, v[f.name]);
+          } else {
+            if (v[f.name] === undefined) {
+              t.writeBinary(dv[i], dv[i].length);
+            } else {
+              vv[i]._write(t, v[f.name]);
+            }
+          }
+        }
+      }
+    })[constructorName];
+    return innerFunction;
+  }
+  return ConstructorFunction(values, dValues);
 };
 
 RecordType.prototype._update = function (resolver, type, opts) {