class301-09.md

Functional Programming

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Definition: Functional programming is a programming model that builds the structure and elements of programs where computation is the evaluation of mathematical functions while avoiding changing-state and mutable data.

Pure Functions:

• Purity:
  • returns the same result given the same arguement (aka deterministic)
  • does not cause obeservable side effects
    • exmaple of observable side effects is increasing the count on a global variable by incrementing the variable inside of the function.
  • passes global objects in as parameters instead of calling them directly inside of the function
  • doesn't read external files
  • doesn't rely on random number generation
• Benefits:
  • code is easier to test
  • doesn't need to mock anything
  • can test with different contexts

Immutability:

• immutable data cannot change its state after it is created
  • you need to create a new object and assign a new value
• recursion can be used to keep our variables immutable

Referential Transparency:

• if a function consistently yields the same result for the same input it is referentially transparent
• this allows for memoizing the function (optimization)
  • replacing the entire expression with a number constant is memoizing

Node.js Modules and require()

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Module - spliting node.js code into separate js files and calling on those files when needed.

Require

• is on the global object in node.js so it can be accessed from anywhere
• allows functions from other files to be accessed
• const variableName = require('./filepath'); don't need .js on the end, it will account for it automatically
• inorder for these file to be accessed in addition to require, they need to be exported module.exports = functionName similarly to React components

Things I want to know more about:

• writing pure functions, and memonizing -- Hard to understand the benefit with the simple example they displayed.