Functional Programming with Javascript

Functional Programming with Javascript

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  Functional Programming With JavaScript DeepankarChopra Senior Software Engineer Ticketmaster
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  » What isFunctional Programming? » Mutations » Side-Effects » Pure Functions » Higher Order Functions » Composition » Advantages & Disadvantages of FP » How does FP differ from Object-Oriented programming 2Overview
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  What is FunctionalProgramming? Functional programming (often abbreviated FP) is the process of building software by » composing pure functions, » avoiding » shared state, » mutable data » side-effects. » Managing state flows through composition 3
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  Mutations Mutable is atype of variable that can be changed after it is created. In JavaScript, only objects and arrays are mutable, not primitive values. (You can make a variable name point to a new value, but the previous value is still held in memory.) 4
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  Mutations 5 let a= { foo: 'bar' }; let b = a; a.foo = 'test’; console.log(a,b); //{foo: "test"} {foo: "test"} // avoiding mutation let a = { foo: 'bar' }; let b = Object.assign({}, a); a.foo = 'test’; console.log(a,b); //{foo: "test"} {foo: "bar"}
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  Side Effects If aprogram / function modifies the state of something else (outside its own scope), then it is producing a side effect. This could effectively include something like "display a character on the screen", or it could be changing the value stored in some arbitrary RAM location, or anything similar. 6
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  Side Effects include »Modifying any external variable or object property (e.g., a global variable, or a variable in the parent function scope chain) » Logging to the console » Writing to the screen » Writing to a file » Writing to the network » Triggering any external process » Calling any other functions with side-effects 7
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  Pure Functions » Mustreturn a value » Can’t produce any side-effects » Must return the same output for a given input 8
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  Pure Functions Example9 let a = 10; function impure1(x) { return x + a; } function impure2(x) { a = 30; return x + a; } console.log(impure1(10));//20 a+=10; console.log(impure1(10));//30 console.log(impure2(10));//40 function pure(x, y) { return x + y; } console.log(pure(10,10));
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  Composition Function Composition isa mathematical concept, by which the result of one function becomes the input of the next, and so on. Composing functions together is like putting together a series of pipes for our data to flow through. 10
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  Composition Example function addOne(x){ return x + 1; } function timesTwo(x) { return x * 2; } console.log(addOne(timesTwo(3))); //7 11
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  Higher Order Functions Ahigher-order function is a function that does at least one of the following: » takes one or more functions as arguments » returns a function as its result. 12
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  Higher Order FunctionsExample function greaterThan(n) { return function(m) { return m > n; }; } let greaterThan10 = greaterThan(10); let greaterThan11 = greaterThan(11); console.log(greaterThan10(11));//true console.log(greaterThan11(11));//false 13
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  Advantages of FP »Pure functions are easier to reason about » Testing is easier, and pure functions lend themselves well to techniques like property-based testing » Debugging is easier » Programs are more bulletproof » Programs are written at a higher level, and are therefore easier to comprehend » Parallel/concurrent programming is easier 14
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  Disadvantages of FP »Not suitable in every situation » Needs to be clubbed with Object oriented programming in some cases. » Makes heavy use of recursion 15
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  How does FPdiffer from OOP 16 Functional Programming » Primary Manipulation Unit is “Function” » Stateless Programming Model » Functions with No-Side Effects » Order of execution is less importance Object Oriented Programming » Primary Manipulation Unit is Objects(Instances of Classes) » Stateful Programming Model » Methods with Side Effects » Order of execution is more important.
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  Any questions? You canmail me at [email protected] 17THANKS!