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Understanding JavaScript Engines and Runtimes
Aug 26, 2024
JavaScript Engines and Runtimes
Overview of JavaScript Engines
Definition
: A JavaScript engine is a computer program that executes JavaScript code.
Examples
:
Google's V8 engine (powers Chrome and Node.js)
Different browsers have their own engines (look up online for more info)
Components of a JavaScript Engine
Call Stack
: Executes code using execution contexts.
Heap
: Unstructured memory pool for storing application objects.
Code Translation: Compilation vs. Interpretation
Compilation
:
Entire source code is converted to machine code at once.
Resulting machine code is saved in a portable file for future execution.
Interpretation
:
Code is executed line by line by an interpreter.
Machine code conversion happens just before execution.
JavaScript's Historical Context
Previously considered a purely interpreted language.
Modern practices have evolved due to performance needs.
Just-in-Time (JIT) Compilation
:
Combines aspects of both compilation and interpretation.
Code is compiled to machine code immediately before execution without portable files.
Execution Process in JavaScript Engines
Parsing
:
JavaScript code is read and converted into an Abstract Syntax Tree (AST).
Syntax errors are checked during this process.
Compilation
:
AST is compiled into machine code.
Code is executed immediately after compilation.
Optimization
:
Initial unoptimized code is executed while background optimizations occur.
Optimized code replaces unoptimized code without stopping execution.
JavaScript Runtime
Definition
: A JavaScript runtime is a container that includes everything needed to execute JavaScript, primarily in a browser context.
Components
:
JavaScript Engine
: Core component that executes code.
Web APIs
: Provide additional functionalities (e.g., DOM manipulation, console logging).
Callback Queue
: Stores callback functions ready for execution.
Event Loop
Manages the Call Stack and Callback Queue.
Executes callbacks when the Call Stack is empty, facilitating non-blocking programming.
Node.js and Other Runtimes
Node.js: A JavaScript runtime outside of the browser.
Lacks web APIs; instead includes C++ bindings and a thread pool.
Conclusion
Understanding JavaScript engines and runtimes is crucial for effective JavaScript development.
Next lecture will cover JavaScript execution in the call stack.
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