JavaScript One-Liners

JavaScript One-Liners.md

1. Get a random boolean (true/false)

const randomBoolean = () => Math.random() >= 0.5;
console.log(randomBoolean());
// Result: a 50/50 change on returning true of false

2. Check if the provided day is a weekday

const isWeekday = (date) => date.getDay() % 6 !== 0;
console.log(isWeekday(new Date(2021, 0, 11)));
// Result: true (Monday)
console.log(isWeekday(new Date(2021, 0, 10)));
// Result: false (Sunday)

3. Reverse a string

const reverse = str => str.split('').reverse().join('');
reverse('hello world');     
// Result: 'dlrow olleh'

4. Check if the current tab is in view / focus

const isBrowserTabInView = () => document.hidden;
isBrowserTabInView();
// Result: returns true or false depending on if tab is in view / focus

5. Check if a number is even or odd

const isEven = num => num % 2 === 0;
console.log(isEven(2));
// Result: true
console.log(isEven(3));
// Result: false

6. Get the time from a date

const timeFromDate = date => date.toTimeString().slice(0, 8);
console.log(timeFromDate(new Date(2021, 0, 10, 17, 30, 0))); 
// Result: "17:30:00"
console.log(timeFromDate(new Date()));
// Result: will log the current time

7. Truncate a number to a fixed decimal point

const toFixed = (n, fixed) => ~~(Math.pow(10, fixed) * n) / Math.pow(10, fixed);
// Examples
toFixed(25.198726354, 1);       // 25.1
toFixed(25.198726354, 2);       // 25.19
toFixed(25.198726354, 3);       // 25.198
toFixed(25.198726354, 4);       // 25.1987
toFixed(25.198726354, 5);       // 25.19872
toFixed(25.198726354, 6);       // 25.198726

8. Check if an element is currently in focus

const elementIsInFocus = (el) => (el === document.activeElement);
elementIsInFocus(anyElement)
// Result: will return true if in focus, false if not in focus

9. Check if the current user has touch events supported

const touchSupported = () => {
  ('ontouchstart' in window || window.DocumentTouch && document instanceof window.DocumentTouch);
}
console.log(touchSupported());
// Result: will return true if touch events are supported, false if not

10. Check if the current user is on an Apple device

const isAppleDevice = /Mac|iPod|iPhone|iPad/.test(navigator.platform);
console.log(isAppleDevice);
// Result: will return true if user is on an Apple device

11. Scroll to top of the page

const goToTop = () => window.scrollTo(0, 0);
goToTop();
// Result: will scroll the browser to the top of the page

12. Get average value of arguments

const average = (...args) => args.reduce((a, b) => a + b) / args.length;
average(1, 2, 3, 4);
// Result: 2.5

13. Convert Fahrenheit / Celsius

const celsiusToFahrenheit = (celsius) => celsius * 9/5 + 32;
const fahrenheitToCelsius = (fahrenheit) => (fahrenheit - 32) * 5/9;
// Examples
celsiusToFahrenheit(15);    // 59
celsiusToFahrenheit(0);     // 32
celsiusToFahrenheit(-20);   // -4
fahrenheitToCelsius(59);    // 15
fahrenheitToCelsius(32);    // 0