Top 50 One-Liners JavaScript

Mastering JavaScript: Top 50 One-Liners Every Developer Should Know

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Introduction:

JavaScript is a versatile and powerful programming language used extensively in web development. Whether you're a seasoned developer or just starting your journey, mastering JavaScript can significantly boost your productivity and efficiency. In this article, we'll explore the top 50 JavaScript one-liners that every developer should know. These concise and elegant solutions cover a wide range of common tasks, from manipulating arrays to working with strings and objects.

1. Checking if a Variable is Undefined:

const isUndefined = variable => typeof variable === 'undefined';

2. Checking if a Variable is Null:

const isNull = variable => variable === null;

3. Checking if a Variable is Empty:

const isEmpty = variable => !variable;

4. Checking if a Variable is an Array:

const isArray = variable => Array.isArray(variable);

5. Checking if a Variable is an Object:

const isObject = variable => typeof variable === 'object' && variable !== null;

6. Checking if a Variable is a Function:

const isFunction = variable => typeof variable === 'function';

7. Getting the Last Element of an Array:

const lastElement = array => array.slice(-1)[0];

8. Flattening an Array:

const flattenArray = array => array.flat();

9. Reversing a String:

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

10. Generating a Random Number:

const randomNumber = (min, max) => Math.floor(Math.random() * (max - min + 1)) + min;

11. Removing Duplicates from an Array:

const removeDuplicates = array => [...new Set(array)];

12. Checking if an Array Contains a Specific Value:

const containsValue = (array, value) => array.includes(value);

13. Checking if a String Contains a Substring:

const containsSubstring = (str, substring) => str.includes(substring);

14. Getting the Current Date and Time:

const currentDateTime = () => new Date().toLocaleString();

15. Checking if a Year is a Leap Year:

const isLeapYear = year => (year % 4 === 0 && year % 100 !== 0) || year % 400 === 0;

16. Truncating a Number to a Specified Decimal Place:

const truncateNumber = (num, decimalPlaces) => Math.trunc(num * 10 ** decimalPlaces) / 10 ** decimalPlaces;

17. Checking if an Object has a Specific Property:

const hasProperty = (obj, property) => obj.hasOwnProperty(property);

18. Converting a String to Title Case:

const toTitleCase = str => str.replace(/\b\w/g, char => char.toUpperCase());

19. Repeating a String N Times:

const repeatString = (str, n) => str.repeat(n);

20. Generating a Range of Numbers:

const range = (start, end) => Array.from({ length: end - start + 1 }, (_, i) => start + i);

21. Summing Numbers in an Array:

const sumArray = array => array.reduce((acc, curr) => acc + curr, 0);

22. Getting the Maximum Value in an Array:

const maxArrayValue = array => Math.max(...array);

23. Getting the Minimum Value in an Array:

const minArrayValue = array => Math.min(...array);

24. Checking if a Number is Even:

const isEven = num => num % 2 === 0;

25. Checking if a Number is Odd:

const isOdd = num => num % 2 !== 0;

26. Checking if a String is Palindrome:

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

27. Reversing the Order of Words in a String:

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

28. Checking if a Number is Prime:

const isPrime = num => {
    for (let i = 2; i <= Math.sqrt(num); i++) {
        if (num % i === 0) return false;
    }
    return num > 1;
};

29. Converting Fahrenheit to Celsius:

const fahrenheitToCelsius = f => (f - 32) * 5 / 9;

30. Converting Celsius to Fahrenheit:

const celsiusToFahrenheit = c => (c * 9 / 5) + 32;

31. Factorial of a Number:

const factorial = n => n === 0 ? 1 : n * factorial(n - 1);

32. Fibonacci Sequence:

const fibonacci = n => n <= 1 ? n : fibonacci(n - 1) + fibonacci(n - 2);

33. Finding the Greatest Common Divisor (GCD) of Two Numbers:

const gcd = (a, b) => b === 0 ? a : gcd(b, a % b);

34. Finding the Least Common Multiple (LCM) of Two Numbers:

const lcm = (a, b) => (a * b) / gcd(a, b);

34. Shuffle an Array:

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

35. Checking if a Number is a Perfect Square:

const isPerfectSquare = num => Math.sqrt(num) % 1 === 0;

36. Checking if a Number is a Power of Two:

const isPowerOfTwo = num => (num & (num - 1)) === 0 && num !== 0;

37. Checking if a Number is a Palindrome:

const isPalindromeNumber = num => num.toString() === num.toString().split('').reverse().join('');

38. Capitalize the First Letter of Each Word in a Sentence:

const capitalizeWords = sentence => sentence.replace(/\b\w/g, char => char.toUpperCase());

39. Counting the Occurrences of Each Element in an Array:

const countOccurrences = array => array.reduce((acc, val) => {
  acc[val] = (acc[val] || 0) + 1;
  return acc;
}, {});

40. Sum of Squares of Digits of a Number:

const sumOfSquareDigits = num => num.toString().split('').reduce((acc, digit) => acc + Math.pow(parseInt(digit), 2), 0);

41. Converting a Number to Binary:

const toBinary = num => num.toString(2);

42. Converting a Binary Number to Decimal:

const binaryToDecimal = binary => parseInt(binary, 2);

43. Checking if a String is an Anagram of Another String:

const isAnagram = (str1, str2) => str1.split('').sort().join('') === str2.split('').sort().join('');

44. Converting an Object to Query Parameters String:

const objectToQueryString = obj => Object.entries(obj).map(([key, value]) => `${encodeURIComponent(key)}=${encodeURIComponent(value)}`).join('&');

45. Checking if a Year is a Leap Year (Using Ternary Operator):

const isLeapYear = year => (year % 4 === 0 && year % 100 !== 0) || year % 400 === 0 ? true : false;

46. Reversing an Array in Place:

const reverseArrayInPlace = array => array.reverse();

47. Finding the Maximum Value in an Array (Using Spread Operator):

const maxArrayValue = array => Math.max(...array);

48. Finding the Minimum Value in an Array (Using Spread Operator):

const minArrayValue = array => Math.min(...array);

49. Truncating a String to a Maximum Length and Appending Ellipsis:

const truncateString = (str, maxLength) => str.length > maxLength ? str.slice(0, maxLength) + '...' : str;

50. Finding the Longest Word in a Sentence:

const longestWord = sentence => sentence.split(' ').reduce((longest, current) => current.length > longest.length ? current : longest, '');

Conclusion:
JavaScript one-liners are concise and powerful solutions to common programming tasks. By mastering these one-liners, you can write cleaner, more efficient code and become a more proficient JavaScript developer. Experiment with these examples and incorporate them into your projects to take your coding skills to the next level. Happy coding!

Comments

[Mike Stemle]

So many of these are wrong. #5 will return true for Date and #13 actually takes more work to use as a one liner than it would just use String.includes().

[Jon Randy 🎖️]

They're wrong because they're most likely straight out of ChatGPT (or similar), and the author has not checked them before posting. Try entering the following into ChatGPT:

Write an article titled "Mastering JavaScript: Top 50 One-Liners Every Developer Should Know"

You'll get many of the same examples, with the same mistakes.

[eerk]

point 7 has been made easer : lastElement = array.at(-1)

[𒎏Wii 🏳️‍⚧️]

As always with these one-liners, whether one should "know" about them or actually use them are two entirely different questions.

To anyone looking at these and thinking about actually using them in real life, here's a couple things to consider:

Obfuscation

Taking a simple comparison like value === undefined (no, you don't need the typeof) and hiding it in a function does almost nothing to shorten the code, but hides what's actually going on, so anyone reading the code will have to jump to the definition instead of just reading what happens.

The same applies to redefining standard functions like const isArray = variable => Array.isArray(variable); (or, if you want to save typing, const {isArray} = Array. If you see Array.isArray(object) you know exactly what it does, or you can directly google it. If you see isArray(object), you'll have to jump to the definition first.

Pointless Code

Looking at an example like this:

const isObject = variable => typeof variable === 'object' && variable !== null;

this could be simplified a fair bit by taking into consideration that something of type 'object' is only falsey if it is null, so this can be shortened to variable && typeof variable == "object"

Use === if it gives you or your linter peace of mind, but typeof always returns a string and the rhs is a constant, so it doesn't really change anything.

An extreme example: Compare flattenArray(array) to array.flat(). You type more by wrapping that in a function, and obfuscate what happens.

Pointless Complexity

The best way to do a thing is sometimes just the straight-forward solution.

If you want to get the last element of an array, just index it with its length + 1, and your code will be much easier to read. You'll also avoid allocating a new single-element array, which would the be up to your VM to optimise away in the best case or to garbage-collect in the worst.

Also, Array.prototype.at() is a thing; you can just use my_array.at(-1) and everyone can understand what it does as long as they know the standard functions well enough.

Other Nitpicks

hasProperty doesn't do what it says and can crash your code:

const p = document.createElement("p")
p.hasOwnProperty("lang") // false
"lang" in p // true

const o = Object.create(null)
"hasOwnProperty" in o // false
Reflect.hasOwnProperty.call(o, "hasOwnProperty") // false
o.hasOwnProperty("hasOwnProperty") // TypeError: o.hasOwnProperty is not a function

The one about the palindrome would be a good starting point for an interview question: How could this function be optimised? The answer is, you only need to compare the first half to the latter half. Mirroring and comparing means every character gets compared twice.

Also that fibonacci function is half a fork bomb. Don't do fibonacci like that, you can literally google how to do it correctly (even recursively) in like 5 minutes.

Same for shuffling an array. That's gonna perform really poorly for large arrays.

Counting the occurrences of an element has a subtle but funny bug because it uses a plain Object without setting its prototype to null:

countOccurrences(["foo", "bar", "foo", "hasOwnProperty"])
// {foo: 2, bar: 1, hasOwnProperty: 'function hasOwnProperty() { [native code] }1'}

For query parameters, just use URLSearchParams:

new URLSearchParams({foo: "foo", bar: "bar"}).toString()
// foo=foo&bar=bar

And lastly, the most nitpicky one of them all: The longest word function will count words followed by a comma as one character longer than they are. Same for any special character, actually.

---

In conclusion, don't take any of these as examples for how to do things. Many of those would make for really good interview questions though. "What can you say about this function?" type stuff.

[Jon Randy 🎖️]

AI generated/assisted posts should adhere to the guidelines for such content.