This document covers key concepts in functional JavaScript including: 1) First class functions, loops, purity, type signatures, partial application, and composition. 2) It discusses the differences between imperative vs declarative programming and defines pure functions. 3) Various exercises are presented to reinforce these functional programming concepts.

1. Functional Js Class

3. First Class Functions

16. Exercises

17. Loops

24. Imperative
vs
Declarative

35. Exercises

36. Type Signatures

44. Type Signatures
• Tell you a “ton” about the function
• Very helpful when doing point free
• http://haskell.org/hoogle/
• http://ttic.uchicago.edu/~dreyer/course/
papers/wadler.pdf (theorems for free)
• https://vimeo.com/28069495 (data driven dev)

45. Purity

46. What’s Impure
• Mutations
• References to things outside the function
• Side effects (logging, db, http, ui)
• Given the same argument, it can give
different output

57. Pure Functions
• Portable
• Parallelizable
• Reusable
• Easily tested
• Easy to reason about

58. Partial Application

64. Curried Function
“A function that takes one
argument at a time”

75. Partial Application
• Build new functions
• “Freeze” state
• Make types “line up”
• Composition

76. Exercises

77. Composition

93. Category Theory
“The mathematical theory of function
composition”
*inaccurate definition

97. Exercises

98. Composition
• Build new functions from other functions
• Declarative
• Mathematically backed
• Cornerstone of functional programs

99. Design

105. Review
• Loops
• First class functions
• Declarative vs Imperative
• Type signatures
• Purity
• Partial application
• Composition
• Module Design