TrinhDinhHuy

Posted on May 21, 2021

10 tips to improve readability in Javascript

#javascript #react

1. Log level and semantic methods

📚 Console docs

console.log("hello world")
console.warn("this is a warning")
console.error("this is an error")
console.info("this is info")
console.debug("this is debug")
console.trace("show trace")

👉 If you try the console.warn, you will get the trace which means that it is easier to debug the code

Let's try other console functions yourself :)

⚠️ Original code

console.log("Error: API key should not be empty")

👉 Refactor

console.error("Error: API key should not be empty")

2. Avoid negative names for boolean variables

😕 It is hard to read double negatives

isStarted 🤜 🤛 isNotStarted

⚠️ Original code

const isInvalidApiKey = apiKey === null

if (isInvalidApiKey) {}

👉 Refactor

const isValidApiKey = apiKey != null

if (!isValidApiKey) {}

3. Avoid flag params

😕 You don't know what the flag params are used for util you have to read the function declaration

⚠️ Original code

renderResult(true)

function renderResult(isAuthenticated) {
    if (isAuthenticated) {
       return <p>App</p>
    } else {
        return <p>Please login</p>
    }

}

🐨 Use object params

renderResult({isAuthenticated: true})

function renderResult({isAuthenticated}) {
    if (isAuthenticated) {
        return <p>App</p>
    } else {
        return <p>Please login</p>
    }

}

🐨 Use 2 functions

function renderAuthenticatedApp() {
    return <p>App</p>
}

function renderUnAuthenticatedApp() {
    return <p>Please login</p>
}

isAuthenticated ? renderAuthenticatedApp() : renderUnAuthenticatedApp()

4. Use guard clauses

😕 Nesting hell

🐨 Make our code fail fast
🐨 Natural flow

if (statusCode === 200) {
    // success
} else {
    if (statusCode === 500) {
        // Internal Server Error
    } else if (statusCode === 400) {
        // Not Found
    } else {
        // Other error
    }
}

if (statusCode === 500) {
    // Internal Server Error
}

if (statusCode === 400) {
    // Not Found
}

if (statusCode !== 200) {
    // Other error
}

// success

5. Make code self-explanatory

🐨 Easy to understand
🐨 Reusable
🐨 A long descriptive name is better than a long comment

// verify that user has added a credit card
function verify(user) {}

function verifyThatUserHasAddedCreditCard(user) {}

⚠️ Original code

 if (country !== 'finland' &&
    country !== 'germany' &&
    country !== 'vietnam' &&
    country !== 'russia' &&
    type !== '💣'
) {
    return Promise.reject('Not available')
}

👉 Refactor

const isInAvailableCountries = (
    country === 'finland' ||
    country === 'germany' ||
    country === 'vietnam' ||
    country === 'russia'
)

const hasBoom = type === '💣'

if (!isInAvailableCountries || hasBoom) {
    return Promise.reject('Not available')
}

🎁 Create a better condition

const availableCountries = ['finland', 'germany', 'vietnam', 'russia']
const isInAvailableCountries = availableCountries.includes(country)

const hasBoom = type === '💣'

if (!isInAvailableCountries || hasBoom) {
    return Promise.reject('Not available')
}

6. Make impossible states impossible

🐨 Easy to understand

🐨 Prevent lots of bugs

📚 Stop using isLoading booleans

isLoading: true
isError: false

isLoading: false
isError: true

// imposible states
isLoading: true
isError: true

const LOADING_STATE = 'LOADING_STATE'
const ERROR_STATE = 'ERROR_STATE'

const state = LOADING_STATE

⚠️ Original code

const [isLoading, setIsLoading] = React.useState(false)
const [error, setError] = React.useState(null)
const [coffee, setCoffee] = React.useState(null)

function handleButtonClick() {
    setIsLoading(true)
    setError(null)
    setCoffee(null)

    getCoffee('cappuccino', 'small', 'finland', true).then(coffee => {
        setIsLoading(false)
        setError(null)
        setCoffee(coffee)
    }).catch(error => {
        setIsLoading(false)
        setError(error)
    })
}

👉 Refactor

const state = {
    idle: 'idle',
    loading: 'loading',
    error: 'error',
    success: 'success',
}

const [error, setError] = React.useState(null)
const [coffee, setCoffee] = React.useState(null)
const [status, setStatus] = React.useState(state.idle) 

function handleButtonClick() {
    setStatus(state.loading)

    getCoffee('cappuccino', 'small', 'finland', true).then(coffee => {
        setStatus(state.success)
        setCoffee(coffee)
    }).catch(error => {
        setStatus(state.error)
        setError(error)
    })
}

7. Use objects for long argument lists

🐨 Params order won't matter

🐨 Easy to pass optional param

function getBox(type, size, price, color) {}

getBox('carry', undefined, 10, 'red')

function getBox(options) {
    const {type, size, price, color} = options
}

getBox({
    type: 'carry',
    price: 10,
    color: 'red'
})

⚠️ Original code

export function getCoffee(type, size, country, hasIce) {

getCoffee('cappuccino', 'small', 'finland', true)
}

👉 Refactor

function getCoffee(options) {
    const {type, size, country, hasIce} = options
}

getCoffee({
    type: 'cappuccino',
    size: 'small',
    country: 'finland',
    hasIce: true
})

8. Use Object.assign for defaults

function getBox(options) {

    options.type = options.type || 'carry'
    options.size = options.size || 'small'
    options.price = options.price || 10
    options.color = options.color || 'red'

    const {type, size, price, color} = options
}

function getBox(customOptions) {

    const defaults = {
        type: 'carry',
        size: 'small',
        price: 10,
        color: 'red',
    }

    const options = Object.assign(defaults, customOptions)

    const {type, size, price, color} = options
}

⚠️ Original code

export function getCoffee(type, size, country, hasIce) {

    type = type || 'cappuccino'
    size = size || 'small'
    country = country || 'finland'
    hasIce = hasIce || false
}

👉 Refactor

function getCoffee(customOptions) {
    const defaultOptions = {
        type: 'cappuccino',
        size: 'small',
        country: 'finland',
        hasIce: false
    }

    const options = Object.assign(defaultOptions, customOptions)
}

function getCoffee(options = {}) {
    const {
        type = 'cappuccino',
        size = 'small',
        country = 'finland',
        hasIce = false
    } = options
}

function getCoffee({
    type = 'cappuccino', 
    size = 'small',
    country = 'finland',
    hasIce = false
} = {}) {
}

9. Replacing switch statements with Object literals

Honestly, I love switch as well and I don't actually know when to use switch statement vs object literals. My feeling just tells me which one to go.

Check out these 2 blogs and decide which one is better for you

📚 Replacing switch statements with Object literals
📚 Switch is ok

const handleSaveCalculation = ({key}) => {
    switch (key) {
        case 'save-copy': {
            saveCopy()
            break
        }
        case 'override': {
            override()
            break
        }
        default:
            throw Error('Unknown action')
    }
}

handleSaveCalculation({key: 'save-copy'})

const handleSaveCalculation = ({key}) => {
    const actions = {
        'save-copy': saveCopy,
        'override': override,
        'default': () => throw Error('Unknown action')
    }

    const action = key in actions ? actions[key] : actions['default']
    return action();
}

handleSaveCalculation({key: 'save-copy'})

⚠️ Original code

let drink
switch(type) {
    case 'cappuccino':
        drink = 'Cappuccino';
        break;
    case 'flatWhite':
        drink = 'Flat White';
        break;
    case 'espresso':
        drink = 'Espresso';
        break;
    default:
        drink = 'Unknown drink';
}

👉 Refactor

const menu = {
    'cappuccino': 'Cappuccino',
    'flatWhite': 'Flat White',
    'espresso': 'Espresso',
    'default': 'Unknown drink'
}

const drink = menu[type] || menu['default']

10. Avoid Hasty Abstractions

😕 I don't know how to create a good abstraction but I've created many bad ones

🐨 prefer duplication over the wrong abstraction

🐨 Nothing is free. The code trades the ability to change requirements for reduced duplication, and it is not a good trade - Dan Abramov

📚 AHA Programming

📚 Goodbye, Clean Code

⚠️ My React Boilerplate

The code below is used to fetch an order and I am using Redux for the state management. What a boilerplate!!! Let's make an abstraction which I will regret later

Fetch an order

// Action Type
const FETCH_ORDERS_START = "FETCH_ORDERS_START";
const FETCH_ORDERS_SUCCESS = "FETCH_ORDERS_SUCCESS";
const FETCH_ORDERS_FAILED = "FETCH_ORDERS_FAILED";

// Action
export const fetchOrder = (token) => {
    return dispatch => {
        dispatch(fetchOrdersStart);
        axios.get('/orders.json?auth=' + token).then(res => {
            dispatch(fetchOrdersSuccess(res));
        }).catch(err => {
            dispatch(fetchOrdersFailed(err));
        });
    };

}

export const fetchOrdersSuccess = (orders) => {
    return {
        type: FETCH_ORDERS_SUCCESS,
        orders: orders,
    };
};

export const fetchOrdersFailed = (error) => {
    return {
        type: FETCH_ORDERS_FAILED,
        error: error,
    };
};

export const fetchOrdersStart = () => {
    return {
        type: FETCH_ORDERS_START,
    };
};

👉️ Abstraction

I dare you understand the abstraction code without clicking the link. And even go to that link, you have to read all the code to understand that abstraction.

If you want to take a deep look into this, checkout AHA Programming and Goodbye, Clean Code

// Action
const moduleName = 'order'
const path = '/order'

const {moduleActionTypes, moduleActions} = useModuleActions(moduleName, path)

function fetchOrder() {
    moduleActionTypes.getModel()    
}

function updateOrder(data) {
    moduleActionTypes.updateModel(data)
}

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Top comments (7)

Adam Nathaniel Davis • May 22 '21

Appreciated this post. I will only add that I personally hate if/else statements when the return could make them obsolete. In practice, this means that I would convert this:

renderResult({isAuthenticated: true})

function renderResult({isAuthenticated}) {
    if (isAuthenticated) {
        return <p>App</p>
    } else {
        return <p>Please login</p>
    }

}

To this:

renderResult({isAuthenticated: true})

function renderResult({isAuthenticated}) {
    if (isAuthenticated) {
        return <p>App</p>
    return <p>Please login</p>
}

And if I'm being really nitpicky, I would personally write it as this:

renderResult({isAuthenticated: true})

function renderResult({isAuthenticated}) {
    return isAuthenticated ? <p>App</p> : <p>Please login</p>;
}

And if I'm really feeling concise, I'd write it as this:

renderResult({isAuthenticated: true})

const renderResult = ({isAuthenticated}) => isAuthenticated ? <p>App</p> : <p>Please login</p>;

Maciej • May 23 '21

@bytebodger The simple if-else usually don't need else so I personally would stick to if + return (first refactor) when the if or else blocks have a few lines. The second and third only if the cases are simple 👍.

@dinhhuyams nice summary :)

Pragmatic Maciej • May 21 '21

Points are mostly valid, outside of this one with switch. Switch is ok

TrinhDinhHuy • May 21 '21 • Edited

Thanks for sharing. To be honest, I love to use switch a lot. Sometimes I prefer Object literals :) I don't know when it is better to use Switch or Object literals. My feeling just tells me which one to go. I added your blog to the Switch section.