I am experimenting with the await keyword in Node.js. I have this test script:
"use strict";
function x() {
return new Promise(function(resolve, reject) {
setTimeout(function() {
resolve({a:42});
},100);
});
}
await x();
But when I run it in node I get
await x();
^
SyntaxError: Unexpected identifier
whether I run it with node or node --harmony-async-await or in the Node.js 'repl' on my Mac with Node.js 7.5 or Node.js 8 (nightly build).
Oddly, the same code works in the Runkit JavaScript notebook environment: https://runkit.com/glynnbird/58a2eb23aad2bb0014ea614b
What am I doing wrong?
Thanks to the other commenters and some other research await can only be used in an async function e.g.
async function x() {
var obj = await new Promise(function(resolve, reject) {
setTimeout(function() {
resolve({a:42});
},100);
});
return obj;
}
I could then use this function as a Promise e.g.
x().then(console.log)
or in another async function.
Confusingly, the Node.js repl doesn't allow you to do
await x();
where as the RunKit notebook environment does.
As others have said, you can't call 'await' outside of an async function. However, to get around this you can wrap the await x(); in an async function call. I.e.,
function x() {
return new Promise(function(resolve, reject) {
setTimeout(function() {
resolve({a:42});
},100);
});
}
//Shorter Version of x():
var x = () => new Promise((res,rej)=>setTimeout(() => res({a:42}),100));
(async ()=>{
try{
var result = await x();
console.log(result);
}catch(e){
console.log(e)
}
})();
This should work in Node 7.5 or above. Also works in chrome canary snippets area.
so as suggested by others await will work inside async. So you can use the below code to avoid using then:
async function callX() {
let x_value = await x();
console.log(x_value);
}
callX();