Composing Software

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Composing SoftwareAn Exploration of Functional Programming and Object Composition in JavaScript

Course Info

This course includes 5 attempts.

All software design is composition: the act of breaking complex problems down into smaller problems and composing those solutions. Most developers have a limited understanding of compositional techniques. It’s time for that to change.

In "Composing Software", Eric Elliott shares the fundamentals of composition, including both function composition and object composition, and explores them in the context of JavaScript. The course covers the foundations of both functional programming and object oriented programming to help the reader better understand how to build and structure complex applications using simple building blocks.

You’ll learn:

• Functional programming
• Object composition
• How to work with composite data structures
• Closures
• Higher order functions
• Functors (e.g., array.map)
• Monads (e.g., promises)
• Transducers
• Lenses

All of this in the context of JavaScript, the most used programming language in the world. But the learning doesn’t stop at JavaScript. You’ll be able to apply these lessons to any language. This course is about the timeless principles of software composition and its lessons will outlast the hot languages and frameworks of today. Unlike most programming books, this one may still be relevant 20 years from now.

The book this course is based on began life as a popular blog post series that attracted hundreds of thousands of readers and influenced the way software is built at many high growth tech startups and fortune 500 companies.

Course Material

• Introduction
• Thank You
• Composing Software: An Introduction
• You Compose Software Every Day
• Composing Functions
• Working Memory
• Signal to Noise Ratio
• Surface Area for Bugs
• Composing Objects
• Conclusion
• Exercise 1
• The Dao of Immutability (The Way of the Functional Programmer)
• Forward
• Exercise 2
• Quiz 13 attempts allowed
• The Rise and Fall and Rise of Functional Programming (Composable Software)
• The Rise of Functional Programming
• Exercise 3
• The Fall of Functional Programming
• The Rise of Functional Programming
• Functional Programming Has Always Been Alive and Well
• Quiz 23 attempts allowed
• Why Learn Functional Programming in JavaScript?
• What JavaScript is Missing
• What JavaScript Has that Pure Functional Languages Lack
• Quiz 33 attempts allowed
• Pure Functions
• What is a Function?
• Exercise 4
• Mapping
• Exercise 5
• Pure Functions
• Exercise 6
• The Trouble with Shared State
• Exercise 7
• Same Input, Same Output
• Exercise 8
• No Side Effects
• Immutability
• Exercise 9
• Conclusion
• Exercise 10
• Quiz 43 attempts allowed
• What is Functional Programming?
• Pure Functions
• Exercise 11
• Function Composition
• Shared State
• Exercise 12
• Immutability
• Exercise 13
• Side Effects
• Exercise 14
• Reusability Through Higher Order Functions
• Exercise 15
• Containers, Functors, Lists, and Streams
• Exercise 16
• Declarative vs Imperative
• Conclusion
• Exercise 17
• Quiz 53 attempts allowed
• A Functional Programmer’s Introduction to JavaScript
• Expressions and Values
• var, let, and const
• Types
• Exercise 18
• Destructuring
• Comparisons and Ternaries
• Exercise 19
• Functions
• Signatures
• Default Parameter Values
• Named Arguments
• Rest and Spread
• Exercise 20
• Currying
• Exercise 21
• Function Composition
• Exercise 22
• Arrays
• Exercise 23
• Method Chaining
• Exercise 24
• Conclusion
• Quiz 63 attempts allowed
• Higher Order Functions
• Exercise 25
• Quiz 73 attempts allowed
• Curry and Function Composition
• What is a curried function?
• Exercise 26
• What is a partial application?
• What’s the Difference?
• Exercise 27
• What is point-free style?
• Exercise 28
• Why do we curry?
• Exercise 29
• Trace
• Exercise 30
• Curry and Function Composition, Together
• Exercise 31
• Conclusion
• Exercise 32
• Quiz 83 attempts allowed
• Abstraction & Composition
• Exercise 33
• Abstraction is simplification.
• Exercise 34
• Abstraction in Software
• Exercise 35
• Abstraction through composition
• Exercise 36
• How to Do More with Less Code
• Exercise 37
• Conclusion
• Exercise 38
• Reduce
• Exercise 39
• Reduce is Versatile
• A Word on Redux
• Exercise 40
• Conclusion
• Quiz 93 attempts allowed
• Abstract Data Types and the Software Crisis
• Common ADT Examples
• Exercise 41
• Why ADTs?
• History of ADTs
• Exercise 42
• Specifications for ADTs
• Exercise 43
• Stack ADT Example
• Definitions
• Abstract Signatures
• Construction
• Stack Operations (operations which return a stack)
• Axioms
• Identity
• Sequence
• Empty
• Exercise 44
• Concrete Implementations
• Exercise 45
• Conclusion
• Exercise 46
• Glossary
• Quiz 103 attempts allowed
• Functors & Categories
• Exercise 47
• Why Functors?
• Exercise 48
• Functor Laws
• Identity
• Composition
• Exercise 49
• Category Theory
• Exercise 50
• Build Your Own Functor
• Exercise 51
• Curried Map
• Exercise 52
• Conclusion
• Exercise 53
• Quiz 113 attempts allowed
• Monads
• Exercise 54
• You’re probably already using monads.
• Exercise 55
• What Monads are Made of
• Exercise 56
• Building a Kleisli Composition Function
• Exercise 57
• The Monad Laws
• Left and right identity laws
• Associativity law
• Identity Laws
• Associativity
• Proving the Monad Laws
• Exercise 58
• Conclusion
• Exercise 59
• Quiz 123 attempts allowed
• The Forgotten History of OOP
• Exercise 60
• The Big Idea
• Exercise 61
• The Essence of OOP
• Exercise 62
• What OOP Doesn’t Mean
• Exercise 63
• What is an object?
• Exercise 64
• We’ve lost the plot.
• Characteristics of Message Passing
• Exercise 65
• Quiz 133 attempts allowed
• Object Composition
• Exercise 66
• What is Object Composition?
• Exercise 67
• Three Different Forms of Object Composition
• Exercise 68
• Notes on Code Examples
• Exercise 69
• Aggregation
• Examples
• When to use
• Considerations
• In Code
• Exercise 70
• Concatenation
• Examples
• When to Use
• Considerations
• In Code
• Exercise 71
• Delegation
• Examples
• When to Use
• Considerations
• In Code
• Exercise 72
• Conclusion
• Exercise 73
• Quiz 143 attempts allowed
• Factory Functions
• Exercise 74
• Literals for One, Factories for Many
• Exercise 75
• Returning Objects
• Exercise 76
• Destructuring
• Exercise 77
• Computed Property Keys
• Default Parameters
• Exercise 78
• Type Inference
• Exercise 79
• Factory Functions for Mixin Composition
• Exercise 80
• Conclusion
• Quiz 153 attempts allowed
• Functional Mixins
• Exercise 81
• Motivation
• Exercise 82
• What are mixins?
• Exercise 83
• What is functional inheritance?
• Exercise 84
• What is a functional mixin?
• Exercise 85
• Composing Functional Mixins
• Exercise 86
• When to Use Functional Mixins
• Exercise 87
• Caveats
• Classes
• Class Performance
• Implicit Dependencies
• Functional Mixins & Functional Programming
• Exercise 88
• Conclusion
• Exercise 89
• Quiz 163 attempts allowed
• Why Composition is Harder with Classes
• Exercise 90
• The Delegate Prototype
• Exercise 91
• The .constructor Property
• Exercise 92
• Class to Factory is a Breaking Change
• Code that Requires new Violates the Open/Closed Principle
• The class Keyword and extends
• Friendly Syntax
• Performance and Memory
• Type Checking
• Class Inheritance with extends
• Classes are OK if You’re Careful
• Exercise 93
• Quiz 173 attempts allowed
• Composable Custom Data Types
• Exercise 94
• You can do this with any data type
• Composable Currency
• Exercise 95
• Quiz 183 attempts allowed
• Lenses
• Exercise 96
• Why Lenses?
• Exercise 97
• Background
• Lens Laws
• Exercise 98
• Composing Lenses
• Over
• Exercise 99
• Quiz 193 attempts allowed
• Transducers
• Exercise 100
• Why Transducers?
• Exercise 101
• Background and Etymology
• A Musical Analogy for Transducers
• Exercise 102
• Transducers compose top-to-bottom.
• Exercise 103
• Transducer Rules
• Initialization
• Early Termination
• Completion
• Exercise 104
• Transducing
• Exercise 105
• The Transducer Protocol
• Exercise 106
• Conclusion
• Exercise 107
• Quiz 203 attempts allowed
• Elements of JavaScript Style
• Exercise 108
• 1. Make the function the unit of composition. One job for each function.
• Exercise 109
• 2. Omit needless code.
• Omit needless variables.
• Exercise 110
• 3. Use active voice.
• Event Handlers
• Lifecycle Methods
• Exercise 111
• 4. Avoid a succession of loose statements.
• Exercise 112
• 5. Keep related code together.
• 6. Put statements and expressions in positive form.
• If Statements
• Ternaries
• Prefer strong negative statements.
• Avoid null and undefined arguments in function calls.
• Exercise 113
• 7. Use parallel code for parallel concepts.
• Exercise 114
• Conclusion: Code should be simple, not simplistic.
• Exercise 115
• Quiz 213 attempts allowed
• Mocking is a Code Smell
• Exercise 116
• TDD should lead to better design.
• Exercise 117
• What is a code smell?
• Exercise 118
• What is a mock?
• Exercise 119
• What is a unit test?
• Exercise 120
• What is test coverage?
• Exercise 121
• What is tight coupling?
• Exercise 122
• What causes tight coupling?
• Exercise 123
• What does composition have to do with mocking?
• Exercise 124
• How do we remove coupling?
• Use pure functions
• Isolate side-effects from the rest of your program logic
• Use pub/sub
• Isolate logic from I/O
• Use objects that represent future computations
• Exercise 125
• “Code smells” are warning signs, not laws. Mocks are not evil.
• Mocking is great for integration tests
• Exercise 126
• Quiz 223 attempts allowed

Instructors

Eric Elliott is a Webby-nominated software engineering expert, author, and creator of SudoLang, an AI programming language. With over 10 years of experience deploying AI models at scale to millions of users, he built and trained production AI models, and was an early pioneer of prompt engineering and AI Driven Development (AIDD). He has served as an engineering manager working on Generative AI for Adobe Firefly, tech lead on a social video AI app spun out of Stanford Research Institute, and a JavaScript expert and consultant on software development productivity and AIDD.

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