Mastering JavaScript Functional Programming: Write clean, robust, and maintainable web and server code using functional JavaScript and TypeScript. 3 Ed

Cover....1 Title Page....2 Copyright and Credits....3 Contributors....5 About the reviewers....6 Table of Contents....8 Preface....14 Chapter 1: Becoming Functional – Several Questions....22 What is functional programming?....22 Theory versus practice....23 A different way of thinking....23 FP and other programming paradigms....24 What FP is not....25 Why use FP?....26 What we need....26 What we get....27 Not all is gold....27 Is JavaScript functional?....28 JavaScript as a tool....28 Going functional with JavaScript....29 Key features of JavaScript....30 How do we work with JavaScript?....36 Using transpilers....38 Working online....40 A step further – TypeScript....40 Testing....43 Summary....43 Questions....43 Chapter 2: Thinking Functionally – A First Example....46 Our problem – doing something only once....46 Solution 1 – hoping for the best!....47 Solution 2 – using a global flag....48 Solution 3 – removing the handler....49 Solution 4 – changing the handler....50 Solution 5 – disabling the button....50 Solution 6 – redefining the handler....51 Solution 7 – using a local flag....51 A functional solution to our problem....52 A higher-order solution....53 Testing the solution manually....56 Testing the solution automatically....56 Producing an even better solution....58 Summary....60 Questions....61 Chapter 3: Starting Out with Functions – A Core Concept....62 All about functions....62 Of lambdas and functions....63 Arrow functions – the modern way....66 Functions as objects....71 Using functions in FP ways....77 Injection – sorting it out....77 Callbacks and promises....81 Continuation-passing style....82 Polyfills....83 Stubbing....87 Immediate invocation (IIFE)....88 Summary....91 Questions....92 Chapter 4: Behaving Properly – Pure Functions....94 Pure functions....94 Referential transparency....95 Side effects....97 Advantages of pure functions....104 Impure functions....109 Avoiding impure functions....110 Is your function pure?....116 Testing – pure versus impure....118 Testing pure functions....118 Testing purified functions....120 Testing impure functions....124 Summary....128 Questions....128 Chapter 5: Programming Declaratively – A Better Style....132 Transformations....133 Reducing an array to a value....133 Applying an operation – map()....141 Dealing with arrays of arrays....148 More general looping....156 Logical HOFs....158 Filtering an array....158 Searching an array....161 Higher-level predicates – every() and some()....164 Checking negatives – none()....165 Working with async functions....166 Some strange behaviors....167 Async-ready looping....169 Working with parallel functions....174 Unresponsive pages....174 A frontend worker....177 A backend worker....180 Workers, FP style....181 Long-living pooled workers....183 Summary....186 Questions....187 Chapter 6: Producing Functions – Higher-Order Functions....190 Wrapping functions – keeping behavior....190 Logging....191 Timing functions....201 Memoizing functions....203 Altering a function’s behavior....214 Doing things once, revisited....214 Logically negating a function....217 Inverting the results....219 Arity changing....221 Throttling and debouncing....223 Changing functions in other ways....225 Turning operations into functions....226 Turning functions into promises....229 Getting a property from an object....231 Demethodizing – turning methods into functions....233 Methodizing – turning functions into methods....236 Finding the optimum....240 Summary....243 Questions....243 Chapter 7: Transforming Functions – Currying and Partial Application....246 A bit of theory....246 Currying....247 Dealing with many parameters....248 Currying by hand....251 Currying with bind()....253 Partial application....257 Partial application with arrow functions....258 Partial application with closures....259 Partial currying....268 Partial currying with bind()....270 Partial currying with closures....273 Final thoughts....274 Variable number of parameters....275 Parameter order....275 Being functional....277 Summary....278 Questions....279 Chapter 8: Connecting Functions – Pipelining, Composition, and More....282 Pipelining....282 Piping in Unix/Linux....283 Revisiting an example....284 Creating pipelines....286 Debugging pipelines....294 Pointfree style....297 Chaining and fluent interfaces....300 An example of fluent APIs....300 Chaining method calls....302 Composing....305 Some examples of composition....306 Composing with higher-order functions....310 Transducing....316 Composing reducers....319 Generalizing for all reducers....321 Testing connected functions....322 Testing pipelined functions....322 Testing composed functions....325 Testing chained functions....326 Testing transduced functions....328 Summary....330 Questions....330 Chapter 9: Designing Functions – Recursion....334 Using recursion....334 Thinking recursively....336 Higher-order functions revisited....346 Searching and backtracking....354 Mutual recursion....362 Odds and evens....362 Doing arithmetic....364 Recursion techniques....369 Tail call optimization....369 Continuation-passing style....372 Trampolines and thunks....377 Recursion elimination....380 Summary....381 Questions....381 Chapter 10: Ensuring Purity – Immutability....386 Going the straightforward JavaScript way....387 Mutator functions....387 Constants....388 Freezing....389 Cloning and mutating....392 Getters and setters....396 Lenses....401 Prisms....413 Creating persistent data structures....417 Working with lists....417 Updating objects....419 A final caveat....425 Summary....425 Questions....426 Chapter 11: Implementing Design Patterns – The Functional Way....430 Understanding design patterns....430 Design pattern categories....431 Do we need design patterns?....433 Object-oriented design patterns....433 Facade and Adapter....434 Decorator or Wrapper....437 Strategy, Template, and Command....441 Dependency Injection....443 Observers and reactive programming....446 Other patterns....458 Functional design patterns....458 Summary....460 Questions....460 Chapter 12: Building Better Containers – Functional Data Types....464 Specifying data types....464 Signatures for functions....465 Other data type options....468 Building containers....470 Extending current data types....471 Containers and functors....473 Monads....488 Functions as data structures....497 Binary trees in Haskell....498 Functions as binary trees....499 Summary....507 Questions....508 Answers to Questions....512 Chapter 1, Becoming Functional – Several Questions....512 Chapter 2, Thinking Functionally – A First Example....518 Chapter 3, Starting Out with Functions – A Core Concept....524 Chapter 4, Behaving Properly – Pure Functions....528 Chapter 5, Programming Declaratively – A Better Style....535 Chapter 6, Producing Functions – Higher-Order Functions....548 Chapter 7, Transforming Functions – Currying and Partial Application....557 Chapter 8, Connecting Functions – Pipelining, Composition, and More....562 Chapter 9, Designing Functions – Recursion....565 Chapter 10, Ensuring Purity – Immutability....575 Chapter 11, Implementing Design Patterns – The Functional Way....583 Chapter 12, Building Better Containers – Functional Data Types....586 Bibliography....598 Index....600 Other Books You May Enjoy....611