Detailed introduction to the running process of Javascript

Javascript is a widely used programming language that can be used to develop interactive pages and applications in a web browser, as well as back-end logic on the server side. Understanding the running process of Javascript can help us better understand how it works and how to write efficient code. This article will introduce the running process of Javascript in detail.

1. Lexical Analysis

When the browser loads a Javascript script, it performs lexical analysis on each line of code. In this process, the browser scans the code character by character and breaks the code into custom units called "tags." Tags are words or symbols in code that have specific meanings, such as variable names, operators, and parentheses.

2. Parsing

Once tokenized, the Javascript engine uses a parser to parse the code. The parser combines tokens into a structural graph called a "syntax tree". The syntax tree defines how the code is executed, the operations to be performed, and their order. For example, if the code contains a function call and a conditional statement, the syntax tree will tell the Javascript engine how to perform these operations in an order and manner.

3. Compilation

Once the syntax tree is created, the Javascript engine will convert it into a more manageable form. This includes optimizing the code, generating bytecode, compiling the code, and loading it into memory for subsequent execution.

4. Execution

The execution process of Javascript code depends on the structure and usage of the code. For example, when code involves operations on the page (such as responding to user input, handling button clicks, and updating elements), the Javascript engine will trigger the execution of the code by calling event handlers. When the code contains loops and conditional statements, the Javascript engine will process them and determine the order of execution from the syntax tree.

5. Optimization

The Javascript engine will also try to optimize the code to improve the performance and response speed of the code. This includes caching results and eliminating unnecessary operations and variable checks while keeping code readable and maintainable. Optimization algorithms for Javascript include dynamic compilation, ahead-of-time computation, and inline caching.

6. Garbage Collection

The Javascript engine also needs to manage the memory allocated during code execution. This is what the garbage collector does. The garbage collector identifies memory that is no longer in use and clears it. This ensures that memory usage is always at a reasonable level and avoids memory leaks and other related problems.

In short, understanding the running process of Javascript helps us better understand how it works and how to write efficient code. When writing Javascript code, you should consider the structure and usage of the code in order to take maximum advantage of the optimization and garbage collection mechanisms of the Javascript engine. At the same time, you should also pay attention to avoid common mistakes and pitfalls, such as infinite loops in loops, variable scopes, and memory leaks.

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