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Welcome to a new module in this course! I am super excited for this one, because now we're going to understand some important concepts in JavaScript. These concepts will later help us provide functionalities to our app like fetching data and sending data to servers. Until now, in this course, we have been dealing with something called synchronous JavaScript, and it's now time to understand asynchronous JavaScript. You might not understand these terms yet, but by the end of this lecture, you will know what they are and why these concepts are crucial to building real-world apps. So, let's get started!
In this lesson, you'll learn about asynchronous JavaScript, a crucial concept for building responsive and efficient applications. Asynchronous JavaScript allows you to perform tasks like fetching data from a server or handling user interactions without blocking the execution of other code.
JavaScript provides several built-in functions that enable you to execute code at specified intervals or after a delay, even while other code is running. This is particularly useful in scenarios like updating a game screen or tracking time on a website.
The setInterval function allows you to execute a block of code repeatedly at specified time intervals. For example, the following code logs "Hello World" every thousand milliseconds:
setInterval(() => {
console.log('Hello World');
}, 1000);
To prevent an interval from running indefinitely, you can store it in a variable and clear it using the clearInterval() function:
const myInterval = setInterval(() => console.log("Hello World"), 1000);
// To stop the interval
clearInterval(myInterval);
The clearInterval function is useful when you want the interval to stop after a certain condition is met.
The setTimeout function allows you to execute a block of code after a specified delay. Unlike setInterval, it only runs once unless set up to repeat. Here's how you use it:
const myTimeout = setTimeout(() => console.log('Hello, World'), 1000); // logs "Hello World" after a thousand ms
// To cancel the timeout
clearTimeout(myTimeout);
The clearTimeout function can be used to cancel the timeout before it executes.
This lesson introduces you to JavaScript code that doesn't execute linearly from top to bottom. Instead, it is asynchronous, meaning that some code can be executed after other code, even if it appears earlier in the file. This is a fundamental concept that allows JavaScript to handle tasks like network requests and user interactions efficiently.
As we continue through the course, you'll delve deeper into asynchronous JavaScript, exploring concepts like promises and async/await, which provide more control and readability when working with asynchronous operations. Understanding these concepts is essential for building real-world applications that are both responsive and efficient.
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