Useful JavaScript Functions

U
Published in: JavaScript

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));
Published in: JavaScript

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Amit Agarwal

Amit Agarwal is a Google Developer Expert in Google Workspace and Google Apps Script. He holds an engineering degree in Computer Science (I.I.T.) and is the first professional blogger in India. He is the developer of Mail Merge for Gmail and Document Studio. Read more on Lifehacker and YourStory

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