Useful JavaScript Functions

The code snippets are from a JavaScript course on Udemy.

  1. Create a function that can be invoked only once.
const once = (fn, ...args) => {
  let called = false;
  return () => {
    if (called === false) {
      called = true;
      return fn(...args);
    }
    return 'Cannot call again';
  };
};

const printName = (text, time) => console.log(`${text} at ${time}`);
const fn = once(printName, 'Google', new Date().toString());

console.log(fn());
console.log(fn());
  1. Measure the time it takes for a JavaScript function to run.
const getUserData = async (user) => {
  const response = await fetch(`https://api.github.com/users/${user}`);
  const json = await response.json();
  return json;
};

const time = (fn, ...args) => {
  console.time('time');
  const result = fn(...args);
  console.timeEnd('time');
  return result;
};

time(() => getUserData('labnol'));
  1. A debounce function that delays invocation until a certain amount of time has passed since the last time that debounce function was invoked.
const debounce = (fn, waitInMs) => {
  let debounced = false;
  return (...args) => {
    if (debounced) clearTimeout(debounced);
    debounced = setTimeout(() => fn(...args), waitInMs);
  };
};

const getWindowLayout = (event) => {
  console.log(event, window.innerHeight, window.innerWidth);
};

window.addEventListener('resize', debounce(getWindowLayout, 500));

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