0.1.4 • Public • Published


Topiarist provides tree and shape-based type verification for JavaScript.

Build Status

You can read the introductory blog post for more information.

A Note on implementation

This library makes liberal use of nonenumerable attributes and Object.getPrototypeOf. It is therefore suitable only for Ecmascript 5 engines. It will work in Ecmascript 6 engines but there would be a much nicer implementation in that case, using Map and private symbols.

Getting It

In Node.js:

npm install --save topiarist


var topiarist = require('topiarist');

For the browser, download the latest release, and refer to it from your script tag:

<script type="text/javascript" src="dist/topiarist.js"></script>


This library provides the following action methods:

  • topiarist.extend(subclass, superclass) which implements classical single inheritance by setting up the prototype chain.
  • topiarist.implement(class, interface) which declares a classes intention to implement an interface, where verification is delayed until after the class has been finalized.
  • topiarist.hasImplemented(class, interface) which declares that a class implements an interface and throws an exception if it does not.
  • topiarist.inherit(class, parent) which provides multiple inheritance by copying functionality from the parent to the class.
  • topiarist.mixin(class, mixin) which provides mixin inheritance, sandboxing mixin methods that are copied onto the class.

and the following query methods:

  • topiarist.isA(instance, parent) which returns true if the instance is of a type which has been declared to be descended from the parent, e.g. because it's extended or implemented or mixed-in.
  • topiarist.classIsA(class, parent) which returns true if the class has been declared to be descended from the parent, e.g. through extension, implementation, etc.
  • topiarist.fulfills(instance, interface) which returns true if the instance supports everything on the interface.
  • topiarist.classFulfills(class, interface) which returns true if instances of the class will be created supporting everything on the interface.

The following convenience methods are also provided:

  • topiarist.install() which copies the appropriate methods onto the Function and Object prototype, renaming them where appropriate. This lets you do things like Subclass.extends(Superclass)
  • topiarist.exportTo() which copies the appropriate methods onto the global object so they can be accessed directly.

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npm i topiarist

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