rfdc

Really Fast Deep Clone

Usage

const clone = require('rfdc')()
clone({a: 1, b: {c: 2}}) // => {a: 1, b: {c: 2}}

API

require('rfdc')(opts = { proto: false, circles: false, constructorHandlers: [] }) => clone(obj) => obj2

proto option

Copy prototype properties as well as own properties into the new object.

It's marginally faster to allow enumerable properties on the prototype to be copied into the cloned object (not onto it's prototype, directly onto the object).

To explain by way of code:

require('rfdc')({ proto: false })(Object.create({a: 1})) // => {}
require('rfdc')({ proto: true })(Object.create({a: 1})) // => {a: 1}

Setting proto to true will provide an additional 2% performance boost.

circles option

Keeping track of circular references will slow down performance with an additional 25% overhead. Even if an object doesn't have any circular references, the tracking overhead is the cost. By default if an object with a circular reference is passed to rfdc, it will throw (similar to how JSON.stringify
would throw).

Use the circles option to detect and preserve circular references in the object. If performance is important, try removing the circular reference from the object (set to undefined) and then add it back manually after cloning instead of using this option.

constructorHandlers option

Sometimes consumers may want to add custom clone behaviour for particular classes (for example RegExp or ObjectId, which aren't supported out-of-the-box).

This can be done by passing constructorHandlers, which takes an array of tuples, where the first item is the class to match, and the second item is a function that takes the input and returns a cloned output:

const clone = require('rfdc')({
  constructorHandlers: [
    [RegExp, (o) => new RegExp(o)],
  ]
})

clone({r: /foo/}) // => {r: /foo/}

NOTE: For performance reasons, the handlers will only match an instance of the exact class (not a subclass). Subclasses will need to be added separately if they also need special clone behaviour.

default import

It is also possible to directly import the clone function with all options set to their default:

const clone = require("rfdc/default")
clone({a: 1, b: {c: 2}}) // => {a: 1, b: {c: 2}}

Types

rfdc clones all JSON types:

• Object
• Array
• Number
• String
• null

With additional support for:

• Date (copied)
• undefined (copied)
• Buffer (copied)
• TypedArray (copied)
• Map (copied)
• Set (copied)
• Function (referenced)
• AsyncFunction (referenced)
• GeneratorFunction (referenced)
• arguments (copied to a normal object)

All other types have output values that match the output of JSON.parse(JSON.stringify(o)).

For instance:

const rfdc = require('rfdc')()
const err = Error()
err.code = 1
JSON.parse(JSON.stringify(e)) // {code: 1}
rfdc(e) // {code: 1}

JSON.parse(JSON.stringify({rx: /foo/})) // {rx: {}}
rfdc({rx: /foo/}) // {rx: {}}

Benchmarks

npm run bench

benchDeepCopy*100: 671.675ms
benchLodashCloneDeep*100: 1.574s
benchCloneDeep*100: 936.792ms
benchFastCopy*100: 822.668ms
benchFastestJsonCopy*100: 363.898ms // See note below
benchPlainObjectClone*100: 556.635ms
benchNanoCopy*100: 770.234ms
benchRamdaClone*100: 2.695s
benchJsonParseJsonStringify*100: 2.290s // JSON.parse(JSON.stringify(obj))
benchRfdc*100: 412.818ms
benchRfdcProto*100: 424.076ms
benchRfdcCircles*100: 443.357ms
benchRfdcCirclesProto*100: 465.053ms

It is true that fastest-json-copy may be faster, BUT it has such huge limitations that it is rarely useful. For example, it treats things like Date and Map instances the same as empty {}. It can't handle circular references. plain-object-clone is also really limited in capability.

Tests

npm test

169 passing (342.514ms)

Coverage

npm run cov

----------|----------|----------|----------|----------|-------------------|
File      |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
----------|----------|----------|----------|----------|-------------------|
All files |      100 |      100 |      100 |      100 |                   |
 index.js |      100 |      100 |      100 |      100 |                   |
----------|----------|----------|----------|----------|-------------------|

__proto__ own property copying

rfdc works the same way as Object.assign when it comes to copying ['__proto__'] (e.g. when an object has an own property key called 'proto'). It results in the target object prototype object being set per the value of the ['__proto__'] own property.

For detailed write-up on how a way to handle this security-wise see https://www.fastify.io/docs/latest/Guides/Prototype-Poisoning/.

Security

Like Object.assign(), rdfc does not offer any protection against prototype poisoning. In other terms, if you clone an object that has a __proto__ property, the target object will have the prototype set.

License

MIT