Front-end interview series five: browser and computer basics

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Preface

This column focuses on explaining the browser/computer basic knowledge interview questions in the interview.

Note: This column will only involve key content and will not be expanded. For some topics that need to expand knowledge points, we will place the expanded content and overall detailed information at the top of each topic, and you can check it by yourself.

Basic knowledge of browser/computer

Basic knowledge of browser/computer
The difference between process and thread
Why JS should be set to single thread
Browser event loop
When to trigger the browser's event loop
The difference between async and defer loading of Script

Problem analysis

The difference between process and thread

• A process is a running program, and a thread is an execution sequence inside the process
• Process is the unit of resource allocation, thread is the unit of execution
• The cost of switching between processes is high, and the cost of switching between threads is small
• Process has more resources, thread has fewer resources
• Multiple threads share the resources of the process

Why JS should be set to single thread

JavaScript reason why 06128634b46884 is single-threaded is related to its purpose. JavaScript is to interact with users and operate DOM . This determines that it can only be single-threaded, otherwise it will bring very complicated synchronization problems. For example, suppose JavaScript has two threads at the same time. One thread DOM node, and the other thread deletes this node. At this time, which thread should the browser use?

Therefore, in order to avoid complexity, JavaScript has been single-threaded since its birth. This has become the core feature of the language and will not change in the future.

Browser event loop

The browser event loop means that when the JS engine parses the JS script, it pushes the synchronous method onto the execution stack and puts the asynchronous method into the event queue. When the method in the execution stack is executed, the browser goes to the event queue to see if There are completed tasks, if there are, they are taken out and placed on the execution stack. Repeating the above actions repeatedly is called an event loop

The answer needs to be linked to the browser thread, that is, JS engine thread, event trigger thread, and timing trigger thread

For more details, please refer to JavaScript operating mechanism detailed explanation:

The difference between async and defer loading of Script

For more details, see The difference between defer and async

Preview of the next section

In the next section, we will bring you the questions of 16128634b469fe handwritten program algorithm questions, so stay tuned!