node.js - NodeJS script with async/await causing syntax error (v7.10.0)

Question

I am trying to use async/await in NodeJS but my script is throwing a syntax error.

I was under the impression that async/await is supported naively since Node 7.6. When I run node -v I get v7.10.0.

Here is the contents of index.js:

async function getValueAsync() {
    return new Promise(function(resolve) {
        resolve('foo');
    });
}

let value = await getValueAsync();
console.log(value);

But when I invoke this script with node index.js I get:

let value = await getValueAsync();
                  ^^^^^^^^^^^^^
SyntaxError: Unexpected identifier
    at createScript (vm.js:53:10)
    at Object.runInThisContext (vm.js:95:10)
    at Module._compile (module.js:543:28)
    at Object.Module._extensions..js (module.js:580:10)
    at Module.load (module.js:488:32)
    at tryModuleLoad (module.js:447:12)
    at Function.Module._load (module.js:439:3)
    at Module.runMain (module.js:605:10)
    at run (bootstrap_node.js:427:7)
    at startup (bootstrap_node.js:151:9)

I am running Linux Mint 18.1.

How can I get my script to compile and run?

Answer 1

await is only valid inside async functions, so you need, for example, an async IIFE to wrap your code with:

void async function() {
  let value = await getValueAsync();
  console.log(value);
}();

And, since return values from async functions are wrapped by a promise, you can shorten getValueAsync to simply this:

async function getValueAsync() {
  return 'foo';
}

Or don't mark it as async and return a promise from it:

function getValueAsync() {
  return new Promise(function(resolve) {
    resolve('foo');
  });
}