Please describe step by step how a JavaScript program executes and who executes the JavaScript program.

When a JavaScript program is executed, it goes through several steps, which can be summarized as follows:

• Loading: The web browser or server-side environment loads the JavaScript file or code into memory.

• Parsing: The JavaScript code is parsed by the browser's JavaScript engine or server-side environment to check for syntax errors and to build an Abstract Syntax Tree (AST) representation of the code.

• Compilation: The JavaScript engine or server-side environment compiles the AST into byte code or machine code, depending on the type of engine being used.

• Execution: The compiled code is executed, and the JavaScript engine or server-side environment follows the instructions in the code to perform the desired tasks. This can include manipulating the Document Object Model (DOM) in a web page, performing calculations, making API calls, and more.

• Garbage Collection: As the program executes, the JavaScript engine or server-side environment keeps track of objects and memory usage, and it performs garbage collection to free up memory that is no longer needed.

• In a web browser, the JavaScript program is executed by the browser's JavaScript engine, which is typically built into the browser. The most common JavaScript engine used in web browsers is V8, which was developed by Google and is used in the Chrome browser and in Node.js.

• In a server-side environment, the JavaScript program is executed by the server, which typically runs a JavaScript runtime environment like Node.js. Node.js uses the V8 engine to execute JavaScript code, and it provides access to a range of built-in modules and APIs that can be used for server-side programming tasks.

• Overall, the JavaScript program is executed by a JavaScript engine or server-side environment, which follows the steps of loading, parsing, compilation, execution, and garbage collection to execute the program and perform the desired tasks.