coding-interview.js

// Functional Lenses
//
// A functional lens is an object that contains 
// two functions, a getter and a setter.
//
// { 
//    getter: (obj) => any, 
//    setter: (obj, value) => obj 
// }
//
// A functional lens provides access to a property of an object.
//
// A functional lens can be used with any of the following functions
//
// view(lens, any) -> returns the value at the lens
// set(lens, value, any) -> returns the object with the changed value at the lens
// over(lens, fn, any) -> returns the object with the changed value at the lens from the output of the function.
//
//
// Instructions
// 1. Write the 3 functions: `view`, `set`, `over` and tests for it
// 2. Looking at propLens create a indexLens that provides similar behavior on an array.

const assert = require('assert');

function propLens (prop) {
  return {
    getter: (obj) => obj[prop],
    setter: (obj, value) => ({ ...obj, [prop]: value })
  }
}

const nameLens = propLens('name')
const person = { name: 'John', last: 'Doe', age: 33 }


console.log(view(nameLens, person))                         // 'John'
console.log(set(nameLens, 'Mary', person))                  // { name: 'Mary', last: 'Doe', age: 33 }
console.log(over(nameLens, v => v.toUpperCase(), person))   // { name: 'JOHN', last: 'Doe', age: 33 }
console.log(person)                                         // { name: 'John', last: 'Doe', age: 33 }