10 one-liners that change how you think about JavaScript

By / Last updated on July 16, 2024

Here’s something most JavaScript developers don’t know:

You can shorten any piece of code into a single line.

With one-liners I went from 17 imperative lines:

JavaScript
// ❌ 17 lines
function extractRedirects(str) {
  let lines = str.split('\n');
  let sourceDestinationList = [];

  for (let line of lines) {
    let sourceDestination = line.split(' ');
    let source = sourceDestination[2];
    let destination = sourceDestination[3];
    let redirectObj = {
      source: source,
      destination: destination,
      permanent: true,
    };
    sourceDestinationList.push(redirectObj);
  }
  
  return sourceDestinationList;
}

To a single functional statement:

JavaScript
// ✅ 1 line -- formatted
const extractRedirects = (str) =>
  str
    .split('\n')
    .map((line) => line.split(' '))
    .map(([, , source, destination]) => ({
      source,
      destination,
      permanent: true,
    }));

The second is so much cleaner and elegant — you can clearly see how the data beautifully flows from input to output with no breaks.

Let’s look at 10 unconventional JS one-liners that push you to the limits of what’s possible with JavaScript.

1. Shuffle array

What do you make of this:

JavaScript
// ✅ Standard Fisher-Yates shuffle, functional version
const shuffleArray = (arr) =>
  [...Array(arr.length)]
    .map((_, i) => Math.floor(Math.random() * (i + 1)))
    .reduce(
      (shuffled, r, i) =>
        shuffled.map((num, j) =>
          j === i ? shuffled[r] : j === r ? shuffled[i] : num
        ),
      arr
    );

// [ 2, 4, 1, 3, 5 ] (varies)
console.log(shuffleArray([1, 2, 3, 4, 5]));

The most complex thing for me was figuring out the immutable no-variable version of the swap — and reduce() has a way of making your head spin.

Then there’s this too:

JavaScript
const shuffleArray = (arr) => arr.sort(() => Math.random() - 0.5);

const arr = [1, 2, 3, 4, 5];

console.log(shuffleArray(arr));

I see it everywhere but it’s terrible for getting a truly uniform distribution.

2. Reverse string

❌ 8 lines:

JavaScript
const reverseString = (str) => {
  let reversed = '';
  for (let i = str.length - 1; i >= 0; i--) {
    const ch = str[i];
    reversed += ch;
  }
  return reversed;
};

const reverse = reverseString('Indestructible!');

console.log(reverse); // !elbitcurtsednI

✅ 1 line:

JavaScript
const reverseString = (str) => str.split('').reverse().join('');

const reverse = reverseString('Indestructible!');
console.log(reverse); // !elbitcurtsednI

3. Group array by ID

Grouping arrays by a specific object property:

JavaScript
const groupBy = (arr, groupFn) =>
  arr.reduce(
    (grouped, obj) => ({
      ...grouped,
      [groupFn(obj)]: [
        ...(grouped[groupFn(obj)] || []),
        obj,
      ],
    }),
    {}
  );

const fruits = [
  { name: 'pineapple🍍', color: '🟡' },
  { name: 'apple🍎', color: '🔴' },
  { name: 'banana🍌', color: '🟡' },
  { name: 'strawberry🍓', color: '🔴' },
];

const groupedByNameLength = groupBy(
  fruits,
  (fruit) => fruit.color
);

console.log(groupedByNameLength);

4. Generate random UUID

So many language concepts working together here:

JavaScript
const generateRandomUUID = (a) =>
  a
    ? (a ^ ((Math.random() * 16) >> (a / 4))).toString(16)
    : ([1e7] + -1e3 + -4e3 + -8e3 + -1e11).replace(
        /[018]/g,
        generateRandomUUID
      );

console.log(generateRandomUUID()); // f138f635-acbd-4f78-9be5-ca3198c4cf34
console.log(generateRandomUUID()); // 8935bb0d-6503-441f-bb25-7bc685b5b5bc

There’s basic arithmetic, powers, random values, methods, bit-shifting, regexes, callback functions, recursion, exponentiation… it’s perfection.

5. Generate random hex color

1 line to generate a random hex color:

JavaScript
const randomHexColor = () =>
  `#${Math.random().toString(16).slice(2, 8).padEnd(6, '0')}`;

console.log(randomHexColor()); // #7a10ba (varies)
console.log(randomHexColor()); // #65abdc (varies)

6. Array equality

Check array equality with a one-liner…

❌ 11 lines:

JavaScript
const areEqual = (arr1, arr2) => {
  if (arr1.length === arr2.length) {
    for (const num of arr1) {
      if (!arr2.includes(num)) {
        return false;
      }
    }
    return true;
  }
  return false;
};

✅ 1 line:

JavaScript
const areEqual = (arr1, arr2) =>
  arr1.sort().join(',') === arr2.sort().join(',');

Or✅:

JavaScript
// For more complex objects
// and sort() will probably have a defined callback
const areEqual = (arr1, arr2) =>
  JSON.stringify(arr1.sort()) === JSON.stringify(arr2.sort());

7. Remove duplicates from array

Shortest way to remove duplicates from an array?

❌ 9 lines:

JavaScript
const removeDuplicates = (arr) => {
  const result = [];
  for (const num of arr) {
    if (!result.includes(num)) {
      result.push(num);
    }
  }
  return result;
};

const arr = [1, 2, 3, 4, 5, 3, 1, 2, 5];

const distinct = removeDuplicates(arr);

console.log(distinct); // [1, 2, 3, 4, 5]

✅ 1 line:

JavaScript
const arr = [1, 2, 3, 4, 5, 3, 1, 2, 5];

const distinct = [...new Set(arr)];

console.log(distinct); // [1, 2, 3, 4, 5]

This used to be like the only reason anyone ever cared for Sets — until we got these 7 amazing new methods.

8. Validate email

Email validation one-liners are all about that regex:

JavaScript
const isValidEmail = (email) =>
  /^[\w-]+(\.[\w-]+)*@([\w-]+\.)+[a-zA-Z]{2,7}$/.test(
    email
  );

console.log(isValidEmail('[email protected]')); // true

console.log(isValidEmail('[email protected]')); // false

console.log(isValidEmail('codingbeautydev.com')); // false

console.log(isValidEmail('hi@')); // false

console.log(isValidEmail('hi@codingbeautydev&12')); // false

But I’ve seen monstrosities like this (more comprehensive):

JavaScript
const isValidEmail = (email) =>
  /^(([^<>()[\]\\.,;:\s@\"]+(\.[^<>()[\]\\.,;:\s@\"]+)*)|(\".+\"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/.test(
    email
  );

console.log(isValidEmail('[email protected]')); // true

console.log(isValidEmail('[email protected]')); // false

console.log(isValidEmail('codingbeautydev.com')); // false

console.log(isValidEmail('hi@')); // false

console.log(isValidEmail('hi@codingbeautydev&12')); // false

And even these (most comprehensive) — can you even see it:

JavaScript
const isValidEmail = (email) =>
  /(?:[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*|"(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21\x23-\x5b\x5d-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])*")@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|\[(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?|[a-z0-9-]*[a-z0-9]:(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21-\x5a\x53-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])+)\])/.test(
    email
  );

console.log(isValidEmail('[email protected]')); // true

console.log(isValidEmail('[email protected]')); // false

console.log(isValidEmail('codingbeautydev.com')); // false

console.log(isValidEmail('hi@')); // false

console.log(isValidEmail('hi@codingbeautydev&12')); // false

It’s probably about being as thorough as possible – let’s say the 1st one catches like 95% of wrong emails, then the 2nd like 99%.

The last one here is actually the official RFC 2822 standard for validating emails – so we’re looking at 100% coverage.

9. Convert JSON to Maps

JavaScript
const jsonToMap = (json) => new Map(Object.entries(JSON.parse(json)));

const json = '{"user1":"John","user2":"Kate","user3":"Peter"}';
const map = jsonToMap(json);

// Kate
console.log(map.get('user2'));

// Map(3) { 'user1' => 'John', 'user2' => 'Kate', 'user3' => 'Peter' }
console.log(map);

10. Convert snake to camel case

Easily convert from snake casing to camel casing with zero temporary variables.

JavaScript
const snakeToCamelCase = (s) =>
  s
    .toLowerCase()
    .replace(/(_\w)/g, (w) => w.toUpperCase().substr(1));

const str1 = 'passion_growth';
const str2 = 'coding_beauty';

console.log(snakeToCamelCase(str1)); // passionGrowth
console.log(snakeToCamelCase(str2)); // codingBeauty

Final thoughts

Countless operations jam-packed into a single statement; A race from input start to output finish with no breaks, a free flow of high-level processing. A testament of coding ability and mastery.

This is the power and beauty of JavaScript one-liners.



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2 thoughts on “10 one-liners that change how you think about JavaScript”

  1. Victor Smirnov

    Example 8 ‘Check if Two Arrays Contain the Same Values’ is incorrect. Please check the test cases below.

    “`javascript
    const areEqual = (arr1, arr2) =>
    arr1.length === arr2.length && arr1.every((num) => arr2.includes(num));

    // Arrays have different items.
    const arrA = [1, 1, 3, 4];
    const arrB = [1, 2, 3, 4];
    console.log(areEqual(arrA, arrB)); // true

    // Arrays have the same items. But the elements occur a different number of times.
    const arr1 = [1, 1, 2, 3, 4];
    const arr2 = [1, 2, 2, 3, 4];
    console.log(areEqual(arr1, arr2)); // true
    “`

    Reply

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