Is javascript automatically interpreted and compiled?

JavaScript is one of the most popular programming languages ​​in the world and is widely used in web development, desktop applications, game development and other fields. During the running of JavaScript, automatic interpretation and compilation will occur, which this article will introduce.

1. Basic concepts of JavaScript interpretation and compilation

Before learning JavaScript, we need to understand the concepts of JavaScript interpretation and compilation.

Explanation: Interpretation means parsing the code line by line during runtime and executing it immediately. Each line of code is parsed once, but only executed once.

Compilation: Compilation means compiling the code into machine language before running it, and then executing the compiled code at runtime. Compilation only needs to be done once and does not need to be compiled again when executing later.

In JavaScript, interpretation and compilation are performed at the same time. This process is called Just-In-Time Compilation. The JavaScript engine parses and compiles the code before it is run, and then executes the compiled code immediately.

2. JavaScript interpretation and compilation

JavaScript interpretation and compilation is completed by the JavaScript engine. There are many kinds of JavaScript engines, including V8, SpiderMonkey, Chakra, etc.

In JavaScript, the processes of interpretation and compilation are carried out at the same time. When JavaScript code is loaded into the browser, the JavaScript engine parses it into an Abstract Syntax Tree (AST), then compiles it into bytecode, and finally converts it into machine language, allowing the computer to Able to execute. This process is called the process of interpretation and compilation.

3. JavaScript optimization

In order to improve the performance of JavaScript, the JavaScript engine will perform some optimizations. The most common optimization techniques include:

1. Inline Caching: The JavaScript engine caches the properties of the accessed object to reduce the number of memory accesses and thereby improve efficiency.
2. Virtualization: JavaScript arrays and objects are often stored discontinuously in memory, which affects performance. To solve this problem, the JavaScript engine virtualizes arrays and objects and stores them in consecutive memory addresses, thereby improving access speed.
3. Just-In-Time Compilation: The JavaScript engine will parse and compile the code before it is run to speed up the execution of the code.
4. Garbage Collection: Variables and objects in JavaScript are often created and destroyed at runtime, and these processes generate garbage. In order to clean up this garbage, the JavaScript engine will periodically perform memory recycling.

4. Summary

The interpretation and compilation of JavaScript is completed by the JavaScript engine. This process is called just-in-time compilation (Just-In-Time Compilation). The JavaScript engine parses and compiles the code before it is run, and then executes the compiled code immediately. In order to improve the performance of JavaScript, the JavaScript engine will perform some optimizations, including inline caching, virtualization, just-in-time compilation, and garbage collection. Mastering the process of interpreting and compiling JavaScript will help us better understand and apply JavaScript programming technology.

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