JavaScript

Utils

// Copy string to clipboard
const copyToClipboard = (str) => navigator.clipboard.writeText(str);

// Capitalize a string
const capitalize = (str) => str.replace(/^\w/, (c) => c.toUpperCase());
// or
// str.charAt(0).toUpperCase() + str.slice(1);

// Reverse an array
arr.reverse(); // Reverses array in-place
arr.concat().reverse(); // Returns a new reversed clone

// Reverse a string
const reverseString = (str) => [...str].reverse().join("");

// Get random item from an array
const getRandomItem = (arr) => arr[Math.floor(Math.random() * arr.length)];

// Get unique values from an array
const getUniqueValues = (arr) => [...new Set(arr)];

// Get sum of numbers in an array
const getSum = (arr) => arr.reduce((a, b) => a + b);

// Get average of numbers in an array
const getAverage = (arr) => arr.reduce((a, b) => a + b) / arr.length;

• Shuffle an array [*]

  // Durstenfeld shuffle
  // Shuffles array in-place
  const shuffleArray = (arr) => {
    for (let i = arr.length - 1; i > 0; i--) {
      const j = Math.floor(Math.random() * (i + 1));
      [arr[i], arr[j]] = [arr[j], arr[i]];
    }
  };
  
  // Simple shuffle (Not properly distributed and inefficient)
  // arr.sort(() => (0.5 - Math.random());

• Format a date string [Intl.DateTimeFormat, toLocaleDateString]

  const formatDate = (dateString) => {
    const options = {
      weekday: "short",
      year: "numeric",
      month: "short",
      day: "2-digit",
      hour: "2-digit",
      minute: "2-digit",
      second: "2-digit",
      hour12: false,
    };
    return new Intl.DateTimeFormat("en", options).format(dateString);
    // or
    // new Date(dateString).toLocaleDateString('en-US', options);
  };
  
  // Usage
  formatDate("1987-07-27T12:34:56"); // Mon, Jul 27, 1987, 12:34:56

• Format a number [Intl.NumberFormat]

  const formatNumber = (number) => {
    const options = {
      notation: "compact",
      compactDisplay: "short",
    };
    return new Intl.NumberFormat("en", options).format(number);
  };
  
  // Usage
  formatNumber(123456); // 123K
  formatNumber(456789012); // 457M

• Convert seconds to HH:MM:SS

  const secToHHMMSS = (sec) => {
    let hours = Math.floor(sec / 3600);
    sec %= 3600;
    let minutes = Math.floor(sec / 60);
    let seconds = Math.floor(sec % 60);
  
    hours = hours < 10 ? `0${hours}` : `${hours}`;
    minutes = minutes < 10 ? `0${minutes}` : minutes;
    seconds = seconds < 10 ? `0${seconds}` : seconds;
  
    return `${hours}:${minutes}:${seconds}`;
  };

• Padding a string [padStart, padEnd]

  "abc".padStart(10); // "       abc"
  "abc".padStart(10, "foo"); // "foofoofabc"
  "abc".padStart(6, "123465"); // "123abc"
  "abc".padStart(8, "0"); // "00000abc"
  
  "abc".padEnd(10); // "abc       "
  "abc".padEnd(10, "foo"); // "abcfoofoof"
  "abc".padEnd(6, "123456"); // "abc123"
  "abc".padEnd(1); // "abc"

Node.js/npm

# List all user installed packages
npm list -g --depth=0

Redirect to another website

[*]

<!-- With HTML `<meta>` tags (not recommended by W3C) -->
<meta http-equiv="refresh" content="0; URL='http://new-website.com'" />

// With JavaScript
window.location = "http://new-website.com"; // or one of these
window.location.href = "http://new-website.com";
window.location.assign("http://new-website.com");
window.location.replace("http://new-website.com");

Misc

• The expression (x = 5, "foo") assigns 5 to x and evaluates to foo.