I'm getting used to the proposed async/await syntax and there's some unintuitive behavior. Inside the "async" function, I can console.log the correct string. However, when I try to return that string, instead, it returns a promise.
Checking this entry: async/await implicitly returns promise? , it's pretty clear that any "async function()" will return a promise, NOT a value. That's fine. But how do you get access to the value? If the only answer is "a callback", that's fine - but I was hoping there might be something more elegant.
// src
// ==========================================
require("babel-polyfill");
var bcrypt = require('bcrypt');
var saltAndHash = function(password){
var hash;
return new Promise(function(resolve, reject){
bcrypt.genSalt(10, function(err, salt) {
bcrypt.hash(password, salt, function(err, hash) {
resolve(hash);
});
});
})
}
var makeHash = async function(password){
var hash = await saltAndHash(password);
console.log("inside makeHash", hash);
return(hash);
}
// from test suite
// ==========================================
describe('Bcrypt Hashing', function(){
it('should generate a hash', function(){
var hash = makeHash('password');
console.log("inside test: ", hash);
should.exist(hash);
})
})
// output to console:
// ==========================================
inside test: Promise {
_d:
{ p: [Circular],
c: [],
a: undefined,
s: 0,
d: false,
v: undefined,
h: false,
n: false } }
inside MakeHash $2a$10$oUVFL1geSONpzdTCoW.25uaI/LCnFqeOTqshAaAxSHV5i0ubcHfV6
// etc
// ==========================================
// .babelrc
{ "presets": ["es2015", "stage-0", "react"] }
Inside an async function, you can use the await keyword before a call to a function that returns a promise. This makes the code wait at that point until the promise is settled, at which point the fulfilled value of the promise is treated as a return value, or the rejected value is thrown.
Define an async function. Use the await operator to await the promise. Assign the result of using the await operator to a variable.
It is the fetch() function that returns a value, which is a Promise instance. It is the Promise instance on which you call the then() method, passing in a callback function, which will be eventually be fired when the async code finishes (and internally, calls resolve() ).
Promise resolve() method: If the value is a promise then promise is returned. If the value has a “then” attached to the promise, then the returned promise will follow that “then” to till the final state. The promise fulfilled with its value will be returned.
Yes, you only can access it using a callback:
makeHash('password').then(hash => console.log(hash));
Or of course, you can just make another async function that waits for it:
it('should generate a hash', async function(){
var hash = await makeHash('password');
console.log("inside test: ", hash);
should.exist(hash);
})
There is no way to access the result of a promise synchronously.
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