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Implement map in javascript

Projecting Arrays

Applying a value to a function and getting a new value is called a projection. To project (transform) one array to another, we have to process each element in the array and collect the results in a new array.

  • We will be solving a problem using Array.prototype.forEach().
  • We will define Array.prototype.map() using Array.prototype.forEach().
  • We will solve the same problem using Array.prototype.map()

This post is a follow up post of the
- Getting started Functional Programming in JavaScript. I would recommend reading that post first.


Project an array of videos into an array of {id, title} pairs using Array.prototype.forEach()

Let's solve with Array.prototype.forEach()

Do notice that the array projections have two operations in common:

  • Traversing the source array
  • Adding each item's projected value to a new array

We can abstract these common operations in Array.prototype.map()

Implement Array.prototype.map() using Array.prototype.forEach()

Lets solve with Array.prtotype.map()

Key Learnings

  • Projection methods iterates over array and creates a new array of projected array element
  • Array.prototype.map() allows you to specify the projection.

Further Reading