JavaScript Async/Await Flashcards For Frontend Developers

Callback hell is a term used to describe the situation where callbacks are nested inside other callbacks, making the code difficult to read and maintain. Developers can use async/await or promises to avoid callback hell. Here is an example code for callback hell:

/* Callback hell */
myFunction(result => {
  anotherFunction(result2 => {
    yetAnotherFunction(result3 => {
      console.log(result3);
    });
  });
});

Async/await is a newer way to handle asynchronous code in JavaScript, and is often considered to be more readable and easier to use than promises. However, it's important to note that async/await is built on top of promises and doesn't replace them. Here is an example code for comparing async/await and promises:

/* Async/await vs promises */
async function myFunction() {
  let result = await fetch("https://api.example.com/data");
  let data = await result.json();
  console.log(data);
}

fetch("https://api.example.com/data")
  .then(result => result.json())
  .then(data => console.log(data));

The Fetch API is a modern way to make HTTP requests in JavaScript. It uses promises to handle the response data. Here is an example code for using the Fetch API:

/* Fetch API */
fetch("https://api.example.com/data")
  .then(response => response.json())
  .then(data => console.log(data));

Debouncing is a technique used to limit the rate at which a function is called, but with a delay between the last invocation and the next invocation. Developers can use setTimeout and clearTimeout to implement debouncing in JavaScript. Here is an example code for debouncing:

/* Debouncing */
let timer;

function myFunction() {
  clearTimeout(timer);
  timer = setTimeout(() => {
    console.log("Function called.");
  }, 1000);
}

window.addEventListener("scroll", myFunction);

The event loop is a mechanism used by JavaScript to handle asynchronous code. It keeps track of all pending operations and executes them in the correct order. Here is an example code for understanding the event loop:

/* Event loop */
console.log("1");
setTimeout(() => console.log("2"), 0);
console.log("3");

When working with asynchronous code, it's important to handle errors that may occur. Developers can use try/catch blocks to handle errors in async/await functions. Here is an example code for error handling:

/* Error handling */
async function myFunction() {
  try {
    let result = await fetch("https://api.example.com/data");
    let data = await result.json();
    console.log(data);
  } catch (error) {
    console.error(error);
  }
}

When working with multiple asynchronous operations, developers can use Promise.all to execute them in parallel. Here is an example code for parallelism:

/* Parallelism */
Promise.all([
  fetch("https://api.example.com/data1"),
  fetch("https://api.example.com/data2"),
])
  .then(results => Promise.all(results.map(result => result.json())))
  .then(data => console.log(data));

Promises are a way to handle asynchronous code in JavaScript. A promise represents a value that may not be available yet, but will be at some point in the future. Here is an example code for creating a promise:

/* Promises */
let promise = new Promise((resolve, reject) => {
  setTimeout(() => resolve("Done!"), 1000);
});

Callbacks are a way to handle asynchronous code in JavaScript. A callback function is passed as an argument to another function and is called when the asynchronous operation is complete. Here is an example code for using callbacks:

/* Callbacks */
function myFunction(callback) {
  setTimeout(() => callback("Done!"), 1000);
}

myFunction(result => console.log(result));

Promises can be chained together to create more complex asynchronous workflows. Here is an example code for chaining promises:

/* Chaining promises */
fetch("https://api.example.com/data")
  .then(result => result.json())
  .then(data => console.log(data));

Async/await is a way to write asynchronous code in a more synchronous style. The async keyword is used to define a function that returns a promise, and the await keyword is used to wait for a promise to resolve before continuing. Here is an example code for using async/await:

/* Async/await */
async function myFunction() {
  let result = await fetch("https://api.example.com/data");
  let data = await result.json();
  console.log(data);
}

When working with multiple asynchronous operations, developers need to be careful of race conditions, where the order of execution is not guaranteed. Developers can use Promise.race to handle race conditions. Here is an example code for race conditions:

/* Race conditions */
Promise.race([
  fetch("https://api.example.com/data1"),
  new Promise((resolve, reject) => setTimeout(() => reject("Timeout!"), 1000)),
])
  .then(result => console.log(result))
  .catch(error => console.error(error));

Throttling is a technique used to limit the rate at which a function is called. Developers can use setTimeout and clearTimeout to implement throttling in JavaScript. Here is an example code for throttling:

/* Throttling */
let timer;

function myFunction() {
  if (!timer) {
    timer = setTimeout(() => {
      console.log("Function called.");
      timer = null;
    }, 1000);
  }
}

window.addEventListener("scroll", myFunction);