JavaScript Engines (V8, SpiderMonkey, JavaScriptCore)
An overview of major JS engines, their architecture, and basic optimization techniques.
Short explanation
JavaScript engines parse, compile, and execute JavaScript code. Modern engines use multiple tiers (interpreter, baseline compiler, JIT compiler) to balance startup speed and runtime performance.
Example: measuring function performance
function sum(n) {
let s = 0;
for (let i = 0; i < n; i++) s += i;
return s;
}
console.time('sum');
sum(1e7);
console.timeEnd('sum');
How JS handles it internally
- Engines parse source code into an AST, then generate bytecode or intermediate representation.
- JIT compilers optimize hot code paths by profiling runtime behavior and emitting faster machine code.
- Optimizations include inlining, hidden classes, and type feedback.
Diagram
Related
🔗 Related:
FAQ
Q: What is JIT?
A: Just-In-Time compilation transforms frequently executed JavaScript into optimized machine code at runtime for speed improvements.