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Discussion on: Functional Programming Principles in JavaScript

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Replies for: JS is fun... const squareIt = (number) => { return number * number; } const myInput = { valueOf() { return performance.now() }} console....

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architectak profile image
Ankit Kumar • 

const squareIt = (number) => {
    return number * number;
}
const myInput = { valueOf() { return performance.now() }}

console.log(performance.now()) // 132161.5
console.log(squareIt(myInput)) // 17466767811.611576
console.log(performance.now()) // 132162
console.log(squareIt(myInput)) // 17466847108.83685
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JS is fun, since input is changing its value on each call, hence output is different

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jonrandy profile image
Jon Randy 🎖️ • • Edited

But the input to the function is the same. The calculation differs because of coercion that happens as a feature if JS. The inputs themselves are unchanged. The input in this case is an object with a single method.

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architectak profile image
Ankit Kumar •

In input of function is function that keeps changes its value, then that function can not be considered as pure function, right ?

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jonrandy profile image
Jon Randy 🎖️ • • Edited

The input is an object, but it's value upon coercion to a number differs on each coercion. In a very strict sense, such a simple function could be considered impure. To make it strictly pure in JS, you could add a bunch of code checking types etc.