Lens

There's a pattern in functional programming called "lenses". fnts brings two necessary functions for this pattern to work, although in a simplified manner, – get and set.

Both of them are similar to what Lodash has to offer, it was just really intereseting to build them on my own.

get

get function can be used to get a value from inside an array/object:

import get from 'fnts/lens/get';

const object = {
  a: {
    b: {
      c: 1
    }
  }
};

const value = get(object, 'a.b.c'); // 1

Morevoer, you can access values deeply nested inside arrays:

import get from 'fnts/lens/get';

const object = {
  a: {
    b: [
      { c: 0 },
      { c: 1 },
      { c: 2 },
      { c: 3 },
    ]
  }
};

const value = get(object, 'a.b.1.c'); // 1

set

Same as with get, you can use dot-notation access on nested object to modify a value at the provided path.

import set from 'fnts/lens/set';

const object = {
  a: {
    b: [
      { c: 0 },
      { c: 1 },
      { c: 2 },
      { c: 3 },
    ]
  }
};

const objectCopy = set(object, 'a.b.1.c', 4);

Returned value will be a deep copy of the original object made using structuredClone which, of course, includes the modified value.

lens

To create lenses themselves, you'd need to use the source-first argument application for get and set:

import get from 'fnts/lens/get';
import set from 'fnts/lens/set';

const object = {
  a: {
    b: [
      { c: 0 },
      { c: 1 },
      { c: 2 },
      { c: 3 },
    ]
  }
};

const objectLens = {
  get: get(object),
  set: set(object),
};

const value = objectLens.get('a.b.1.c'); // 1
const objectCopy = objectLens.set('a.b.1.c', 4);

Or, simply use the lens function!

import lens from 'fnts/lens';

const object = {
  a: {
    b: [
      { c: 0 },
      { c: 1 },
      { c: 2 },
      { c: 3 },
    ]
  }
};

const objectLens = lens(object);

const value = objectLens('a.b.1.c'); // 1
const objectCopy = objectLens('a.b.1.c', 4);