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Discussion on: 5 ways to refactor if/else statements in JS functions

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aminnairi profile image
Amin • Edited

Hi there, great article, thank you!

I like to deal with all the error cases first, and then dealing with the heart of the function. Also I like to create small functions that deal with a single responsibility, this is easier to work with IMO.

I have sort of a kink with promises now and I like to put them everywhere. I like the simplicity of chaining functions.

"use strict";

const string = something => JSON.stringify(something);

const divide = (numerator, denominator) => new Promise((resolve, reject) => {
    if (typeof numerator !== "number") {
        return reject(new TypeError(`numerator should be a number in divide(${string(numerator)}, ${string(denominator)})`));
    }

    if (typeof denominator !== "number") {
        return reject(new TypeError(`denominator should be a number in divide(${string(numerator)}, ${string(denominator)})`));
    }

    if (0 === denominator) {
        return reject(new Error(`denominator should not be zero in divide(${string(numerator)}, ${string(denominator)})`));
    }

    return resolve(numerator / denominator);
});

divide(1, 2)
    .then(result => divide(result, 2))
    .then(result => divide(result, 2))
    .then(result => console.log(`After dividing by two three times: ${result}.`))
    // After dividing by two three times: 0.125.
    .catch(({message}) => console.error(`error while dividing: ${message}.`));

divide(1, 0)
    .then(result => divide(result, 2))
    .then(result => divide(result, 2))
    .then(result => console.log(`After dividing by two three times: ${result}.`))
    .catch(({message}) => console.error(`error while dividing: ${message}.`));
    // error while dividing: denominator should not be zero in divide(1, 0).
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dhintz89 profile image
Daniel Hintz

This is an awesome demonstration! I need to start learning and living this pattern for larger functionality.

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rasmusvhansen profile image
rasmusvhansen

I am not sure turning inherently synchronous code into async is a good idea. Promises are OK (not great - observables are better in many cases) for async operations but I would definitely avoid introducing the complexity for inherently sync operations.

By using this pattern, you are forcing all your code to be async.

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sylwiavargas profile image
Sylwia Vargas Author

THANK YOU! YES, I was soooo tempted to touch on Promises but then majority of folks who read my blogs (maybe less so now?) are beginners so I'm planning to write a separate thing on promises in general. However, I'll link your comment in the article because I love your example! Thank you.

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eecolor profile image
EECOLOR

If you use async your code becomes a bit more natural:

async function divide(numerator, denominator) {
    if (typeof numerator !== "number") {
        throw new TypeError(`numerator should be a number in divide(${numerator}, ${denominator})`);
    }

    if (typeof denominator !== "number") {
        throw new TypeError(`denominator should be a number in divide(${numerator}, ${denominator})`);
    }

    if (0 === denominator) {
        throw new Error(`denominator should not be zero in divide(${numerator}, ${denominator})`);
    }

    return numerator / denominator;
});
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This however indicates that it would be probably be smart to remove the async and move that to a separate function. That would allow you to use the divide function in more scenario's.