JSNation 2019: Stop the Software Apocalypse with Functional Programming

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Stop the Software Apocalypse with Functional Programming

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Somers, J. (2017). The Coming Software Apocalypse. The Atlantic.

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Reduce complexity with pure functions

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Mutability let counter = x + 3; // counter = 7 console.log(counter + x); // 25

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let counter = x + 3; // counter = 7 console.log(counter + x); // 25 Where is x changing? Side effects

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No side effects function getX(value) { return value + 2; } getX(2); // 4 getX(5); // 7

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function getX(value) { return value + 2; } getX(2); // 4 getX(5); // 7 No mutation Different input

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Optimize for correctness

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Tests describe("...", function() { beforeEach(function() { // prepare the state }); context("when...", function() { it("returns...", function() { // expects something }); }); afterEach(function() { // clean the state }); });

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Tests describe("...", function() { context("when value is 2", function() { it("returns...", function() { return expect(getX(2)).to.be.equal(4); }); }); });

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Types function changeProperty(property) { return property.toUpperCase(); } const user = { name: "Joe", age: 50 };

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Types function changeProperty(property) { return property.toUpperCase(); } const user = { name: "Joe", age: 50 }; changeProperty(user.email)

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Types changeProperty(user.email)

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Types interface User { name: string; age: number; } function changeProperty(property: string): string { return property.toUpperCase(); } const user: User = { name: "Joe", age: 50 }