to-fast-properties 
Force V8 to use fast properties for an object
Use %HasFastProperties(object) and --allow-natives-syntax to check whether an object already has fast properties.
Install
$ npm install --save to-fast-properties
Usage
const toFastProperties = require('to-fast-properties');
const obj = {
foo: true,
bar: true
};
delete obj.foo;
// `obj` now has slow properties
toFastProperties(obj);
// `obj` now has fast properties
License
MIT © Petka Antonov, John-David Dalton, Sindre Sorhus