Lentes
Lentes is an idiomatic TypeScript library for constructing fully typed lenses, a nice functional design pattern for navigating and transforming immutable objects, in a declarative and string-free way.
Installation
Lentes is available on npm, just add it to your project's dependencies:
# if you use npm npm install lentes --save # or, if you rather use yarn yarn add lentes
So... What are lenses?
This library works around the idea of Lenses. You can think of lens as a bidirectional transform function that can be used to read or update a field nested deep inside an immutable object. So instead of doing this:
you can do this:
Lenses might also be used to replace harcoded strings as object identifiers. This is specially useful to link objects in separate graphs:
// Instead of the error-prompt alternative:createTextBox // You can writecreateTextBox
Usage
Use the default export of the library to build root lenses:
// You can create lenses from a type... // ...or a class instance... // ...or any other object.
Lenses expose the same properties as the types they are built from, which can be used to build new lenses pointing to those properties:
// This lens points to the z field of the second entry in the ys array of the x field of yourObject.
Notice how you can build lens to a certain element of an array by accessing it's index on the array lens. Also, since lens are fully typed, you can navigate their interface aided by your favorite IDE autocomplete and invalid accesses will be rejected by the typechecker.
Once you have a lens, you can either apply it with a single argument to retrieve the pointed value or apply with a second argument to obtain a copy of the object with that property updated:
lyourObject // returns 2lyourObject, 7 // returns { x: { ys: [{z: 1}, {z: 7}, {z: 3}] } }
Alternatively, you can use a function as second argument. If so, the object will be updated with the result of applying that function to the current value:
lyourObject, // returns { x: { ys: [{z: 3}] } }
Lenses also convert to sensible strings that can be used as local ids:
// All these lines return "/x/ys/0/z/"l.toStringl.toPrimitive``
Contributions
Please report any bugs, requests or ideas on the issues section of this repository and we will try to see to it as soon as possible. Pull requests are always welcome! Just try to keep them small and clean.
License
This code is open source software licensed under the ISC License by The Uqbar Foundation. Feel free to use it accordingly.