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denoland-deno/core/examples/eval_js_value.rs
Matt Mastracci a1764f7690
refactor(core): Improve ergonomics of managing ASCII strings (#18498)
This is a follow-on to the earlier work in reducing string copies,
mainly focused on ensuring that ASCII strings are easy to provide to the
JS runtime.

While we are replacing a 16-byte reference in a number of places with a
24-byte structure (measured via `std::mem::size_of`), the reduction in
copies wins out over the additional size of the arguments passed into
functions.

Benchmarking shows approximately the same if not slightly less wallclock
time/instructions retired, but I believe this continues to open up
further refactoring opportunities.
2023-04-04 06:46:31 -06:00

48 lines
1.4 KiB
Rust

// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
//! This example shows you how to evaluate JavaScript expression and deserialize
//! return value into a Rust object.
// NOTE:
// Here we are deserializing to `serde_json::Value` but you can
// deserialize to any other type that implementes the `Deserialize` trait.
use deno_core::v8;
use deno_core::JsRuntime;
use deno_core::RuntimeOptions;
fn main() {
let mut runtime = JsRuntime::new(RuntimeOptions::default());
// Evaluate some code
let code = "let a = 1+4; a*2";
let output: serde_json::Value =
eval(&mut runtime, code).expect("Eval failed");
println!("Output: {output:?}");
let expected_output = serde_json::json!(10);
assert_eq!(expected_output, output);
}
fn eval(
context: &mut JsRuntime,
code: &'static str,
) -> Result<serde_json::Value, String> {
let res = context.execute_script_static("<anon>", code);
match res {
Ok(global) => {
let scope = &mut context.handle_scope();
let local = v8::Local::new(scope, global);
// Deserialize a `v8` object into a Rust type using `serde_v8`,
// in this case deserialize to a JSON `Value`.
let deserialized_value =
serde_v8::from_v8::<serde_json::Value>(scope, local);
match deserialized_value {
Ok(value) => Ok(value),
Err(err) => Err(format!("Cannot deserialize value: {err:?}")),
}
}
Err(err) => Err(format!("Evaling error: {err:?}")),
}
}