V8’s Ignition is responsible for converting the Abstract Syntax Tree (AST) of JavaScript code into bytecode. But instead of compiling the entire code to machine code right away, Ignition first creates a compact intermediate representation (bytecode). This helps speed up the initial execution of code, enabling the program to start running faster.
Bytecode Generation: Ignition takes the parsed JavaScript (represented as an AST) and translates it into bytecode, a simpler form that's quick to interpret and execute. This allows the engine to avoid the delays of full compilation at the start.
Efficient Interpretation: The bytecode generated by Ignition is not directly machine code, but it’s much more efficient to execute than raw JavaScript. This enables fast initial execution while allowing the V8 engine to keep working on optimizing performance in the background.
Fast Startup: Ignition’s role is to make sure JavaScript code can be executed quickly after being parsed, without having to wait for the full JIT compilation to be done. This results in faster startup times, especially for smaller code snippets.
In short, Ignition helps V8 process JavaScript code efficiently at runtime by first converting it into bytecode, ensuring that code can start running quickly while still leaving room for optimization later on with TurboFan.