Comment by speps

People who need an extremely high performance JavaScript engine, where the extra performance is worth using an engine that's hard to embed, has an unstable API, and an absolutely massive unwieldy Google-style C++ code base with all the pain that entails, plus a JIT and all the limitations that entails, JITed V8 is the right choice.

People who just want to run JavaScript code where performance isn't such a big concern would prefer something like Boa (or the other engines listed on the comparison benchmark page).

Both have their uses, and their use case is almost entirely non-overlapping. You wouldn't choose Boa for a competitive web browser engine or as the runtime for your back-end server software. You would consider it for a plug-in system, or maybe a game's scripting system.

It isn't, v8 will have anywhere between 2-1000x performance depending on the exact code it's jitting. Boa absolutely destroys v8 here though:

    use boa_engine::{Context, Source, JsResult};
    
    fn main() -> JsResult<()> {
      let js_code = r#"
          let two = 1 + 1;
          let definitely_not_four = two + "2";
    
          definitely_not_four
      "#;
    
      // Instantiate the execution context
      let mut context = Context::default();
    
      // Parse the source code
      let result = context.eval(Source::from_bytes(js_code))?;
    
      println!("{}", result.display());
    
      Ok(())
    }

Is it though? V8 and spider monkey both have jits so performance numbers of the form “wow V8 is vastly faster than any of these other ones!” (similarly for sm). Does that really have any value?