How to FP

Functional programming in JavaScript is easy.

Easier, in fact, than OOP in JavaScript.

If you've been looking at academic discourses about functional programming with terms such as referential transparency, lambda calculus, and the dreaded monad, then it's no wonder you're confused. But you don't need to understand any of that terminology (or even the theory) to FP.

Here we present the fundamental techniques for functional programming without all the painful academic theory and terminology. You, too, can FP.

How to FP

• Functions are the basic unit of reusability
  • Given the same arguments, a function must return the same result
  • Functions take at least one parameter
  • Functions return exactly one result
  • Functions can be passed as arguments to other functions
  • Functions can be returned from other functions
  • Functions can call functions, including themselves
  • Don't be reaching outside the function to mess with shit
  • Make copies when passing by reference
  • Functions can remember things for you
• Variables are “set and forget”
  • Use const exclusively!
  • Assign variables when they are declared
  • Once a variable has been assigned, don't be changing it
  • Don't erase state: create new state instead!
  • Use destructuring and the rest/spread operators to make copies
• Loops are so last millennium!
  • Functions can call themselves! No, really!
  • Use map to modify each value in a list
  • Use reduce to combine elements in a list
  • More fun with reduce
  • Use filter to choose particular values from a list
  • Use adjust to update a single value in a list
  • Use append, insert, or prepend to add an item to a list
  • Use remove to remove an item from a list
  • Use concat or zip to combine two lists
  • Use times to create a new list
  • Use head and tail to destructure a list
  • Use all, any, or none to test a list
  • Use flatten to flatten nested lists into a single list
  • Avoid forEach! Avoid forEach! Avoid forEach!
• We can has pipelines!
  • Use curry to make functions that make functions
  • Use pipe or compose to combine functions into pipelines
  • Think in terms of state!