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The JavaScript Interview Handbook: 100+ Interview Questions

Solution Review: Club Entry System

Explore how to implement function composition by combining filter and map methods to process customer data for club entry. Understand the use of reduceRight for right-to-left function application and learn how to filter and map arrays effectively with functional programming in JavaScript.

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Solution review

Node.js
const filter = func => arr => arr.filter(func);
const map = func => arr => arr.map(func);
const funcCompose = (...funcs) => args => funcs.reduceRight((arg, fn) => fn(arg), args);
function test(customers){
  const ans = funcCompose(
  map(x => x.name),
  filter(x => x.age >= 18)
  )(customers)
  return ans
}
const customers = [ { name: "Hermoine", age: 15 },
    { name: "Ron", age: 18 }, 
    { name: "Harry", age: 24 },]
console.log(test(customers))

Explanation

You were given two functions, filter and map (lines 1 & 2).

  • filter applies the function, func, on each element of the array, arr, on which it is called.

  • map applies the function, func, on each element of the array, arr, on which it is called.

On line 4, we define our funcCompose ...