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// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
//! This example shows you how to define ops in Rust and then call them from
//! JavaScript.
use deno_core::op_sync;
use deno_core::JsRuntime;
use std::io::Write;
fn main() {
// Initialize a runtime instance
let mut runtime = JsRuntime::new(Default::default());
// The first thing we do is define two ops. They will be used to show how to
// pass data to Rust and back to JavaScript.
//
// The first one is used to print data to stdout, because by default the
// JavaScript console functions are just stubs (they don't do anything).
//
// The second one just transforms some input and returns it to JavaScript.
// Register the op for outputting a string to stdout.
// It can be invoked with Deno.core.dispatch and the id this method returns
// or Deno.core.dispatchByName and the name provided.
runtime.register_op(
"op_print",
// The op_fn callback takes a state object OpState,
// a structured arg of type `T` and an optional ZeroCopyBuf,
// a mutable reference to a JavaScript ArrayBuffer
op_sync(|_state, msg: Option<String>, zero_copy| {
let mut out = std::io::stdout();
// Write msg to stdout
if let Some(msg) = msg {
out.write_all(msg.as_bytes()).unwrap();
}
// Write the contents of every buffer to stdout
if let Some(buf) = zero_copy {
out.write_all(&buf).unwrap();
}
Ok(()) // No meaningful result
}),
);
// Register the JSON op for summing a number array.
runtime.register_op(
"op_sum",
// The op_sync function automatically deserializes
// the first ZeroCopyBuf and serializes the return value
// to reduce boilerplate
op_sync(|_state, nums: Vec<f64>, _| {
// Sum inputs
let sum = nums.iter().fold(0.0, |a, v| a + v);
// return as a Result<f64, AnyError>
Ok(sum)
}),
);
// Now we see how to invoke the ops we just defined. The runtime automatically
// contains a Deno.core object with several functions for interacting with it.
// You can find its definition in core.js.
runtime
.execute(
"<init>",
r#"
// First we initialize the ops cache.
// This maps op names to their id's.
Deno.core.ops();
// Then we define a print function that uses
// our op_print op to display the stringified argument.
const _newline = new Uint8Array([10]);
function print(value) {
Deno.core.dispatchByName('op_print', 0, value.toString(), _newline);
}
"#,
)
.unwrap();
// Now we can finally use this in an example.
runtime
.execute(
"<usage>",
r#"
const arr = [1, 2, 3];
print("The sum of");
print(arr);
print("is");
print(Deno.core.opSync('op_sum', arr));
// And incorrect usage
try {
print(Deno.core.opSync('op_sum', 0));
} catch(e) {
print('Exception:');
print(e);
}
"#,
)
.unwrap();
}
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