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⭐ Introduction to the column
Front-end Getting Started Tour: Explore the wonderful world of Web development Remember to click the link above or on the right to subscribe to this column Oh Geometry will take you on a front-end journey
Welcome to the front-end introductory tour! This column is tailored for those friends who are interested in web development and have just stepped into the front-end field. Whether you are a complete novice or have some basic developers, here will provide you with a systematic and friendly learning platform. In this column, we will update it every day in the form of questions and answers, presenting selected front-end knowledge points and answers to frequently asked questions. Through the question-and-answer format, we hope to more directly respond to readers' questions about front-end technology, and help everyone gradually build a solid foundation. Whether it's HTML, CSS, JavaScript, or a variety of commonly used frameworks and tools, we'll explain concepts in simple terms and provide practical examples and exercises to reinforce what you've learned. At the same time, we will also share some practical tips and best practices to help you better understand and use various technologies in front-end development.
Not only that, we also regularly launch some practical project tutorials, so that you can apply the knowledge you have learned to actual development. Through the practice of actual projects, you will be able to better understand the workflow and methodology of front-end development, and develop your ability to solve problems and develop independently. We believe that only by continuous accumulation and practice can we truly master front-end development technology. So get ready for the challenge and bravely embark on this front-end introductory journey! Whether you're looking for a career transition, upskilling or personal interest, we're committed to providing you with the highest quality learning resources and support. Let's explore the wonderful world of web development together! Join the front-end introductory journey and become an excellent front-end developer! Let's set sail on the front-end journey
The Event Loop in JavaScript is an important mechanism for managing the execution of asynchronous code. It ensures that tasks are executed in the correct order in a JavaScript single-threaded environment, while allowing asynchronous operations such as timers, network requests, and event handling.
The mechanism of the event loop can be divided into the following important parts:
⭐ Call Stack
The call stack is a data structure used to manage function calls. When you call a function, the function is pushed onto the call stack, indicating that it is executing. When the function finishes executing, it is popped from the call stack. This is a last-in-first-out (LIFO) data structure.
⭐ Message Queue
Message queues are used to store pending messages or tasks. These messages are usually produced by asynchronous operations such as timers, event handlers, network requests, etc. Each message contains a callback function and associated information.
⭐ Event Loop
The event loop is a continuously running process that constantly checks the call stack and message queue. Its workflow is as follows:
- Check whether the call stack is empty, if it is empty, wait until a new task enters.
- If the call stack is not empty, check the message queue for pending messages.
- If there is a message in the message queue, the event loop will push the callback function in the message into the call stack for execution.
- After the callback function is executed, it is popped from the call stack and continues to check for the next message in the message queue.
- This process is repeated to ensure that asynchronous tasks are executed at the right time.
⭐ Macro and micro tasks
In the message queue, tasks can be divided into two types: macro task (macro task) and micro task (micro task):
- Macrotasks include timer callbacks, event handlers, I/O operations, etc., which are pushed into the message queue for execution.
- Microtasks include Promise callback functions,
async/awaitasynchronous functions, etc. Their priority is higher than that of macrotasks, and they will be executed immediately after the execution of the current macrotask.
In the event loop, all microtasks are executed first, followed by macrotasks. This ensures that microtasks can be executed before the next macrotask starts, helping to respond faster to asynchronous operations.
⭐ example
Here is a simple example demonstrating the workflow of the event loop:
console.log("Start");
setTimeout(function () {
console.log("Timeout");
}, 0);
Promise.resolve().then(function () {
console.log("Promise");
});
console.log("End");
The output order will be:
- “Start”
- “End”
- “Promise”
- “Timeout”
In this example, the setTimeout callback is queued to the macrotask, and the Promise callback is queued to the microtask. Therefore, microtasks are executed before macrotasks.
In short, the event loop is one of the core mechanisms of JavaScript asynchronous programming, which ensures the orderly execution of asynchronous tasks and enables asynchronous operations in JavaScript single-threaded environments.
⭐ Written at the end
This column is suitable for a wide range of readers, suitable for front-end beginners; or partners who have never studied the front-end and are interested in the front-end, or back-end students who want to better show themselves and expand some front-end knowledge points during the interview process, so If you have a front-end foundation and follow this column to learn, it can also help you to check and fill in the gaps to a great extent. Since the blogger himself does the content output, if there are any flaws in the article, you can contact me on the left side of the homepage , we make progress together, and at the same time recommend several columns for everyone, interested partners can subscribe: In addition to the columns below, you can also go to my homepage to see other columns;
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