core(examples): Deserialize the result of execute_script (#12806)

Example of transforming execute_script response to a serde_json::Value

Co-authored-by: Bartek Iwańczuk <biwanczuk@gmail.com>

core/examples/eval_js_value.rs

@@ -0,0 +1,48 @@
+// Copyright 2018-2021 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: &str,
+) -> Result<serde_json::Value, String> {
+  let res = context.execute_script("<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)),
+  }
+}