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Promises - How to make asynchronous code execute synchronous without async / await?

var p1 = new Promise(function(resolve, reject) {
setTimeout(() => resolve("first"), 5000);
});
var p2 = new Promise(function(resolve, reject) {
setTimeout(() => resolve("second"), 2000);
});
var p3 = new Promise(function(resolve, reject) {
setTimeout(() => resolve("third"), 1000);
});
console.log("last to print");
p1.then(()=>p2).then(()=>p3).then(()=> console.log("last to be printed"))
As I was reading about promises, I know that I can print promises synchronous (in this case print: first, second, third, last to print) when I use async /await. Now I have also been reading that the same thing can be achieved using .then chaining and async/await is nothing 'special'. When I try to chain my promises, however, nothing happens except for the console.log of "last to be printed". Any insight would be great! Thanks!!
Edit to question:
var p1 = new Promise(function (resolve, reject) {
setTimeout(() => console.log("first"), 5000);
resolve("first resolved")
});
var p2 = new Promise(function (resolve, reject) {
setTimeout(() => console.log("second"), 2000);
resolve("second resolved")
});
var p3 = new Promise(function (resolve, reject) {
setTimeout(() => console.log("third"), 0);
resolve("third resolved")
});
console.log("starting");
p1.then((val) => {
console.log("(1)", val)
return p2
}).then((val) => {
console.log("(2)", val)
return p3
}).then((val) => {
console.log("(3)", val)
})
Loggs:
starting
(1) first resolved
(2) second resolved
(3) third resolved
third
second
first
1: if executor function passed to new Promise is executed immediately, before the new promise is returned, then why are here promises resolved ()synchronously) first and after the setTimeouts (asynchronously) gets executed?
Return value vs. resolve promise:
var sync = function () {
return new Promise(function(resolve, reject){
setTimeout(()=> {
console.log("start")
resolve("hello") //--works
// return "hello" //--> doesnt do anything
}, 3000);
})
}
sync().then((val)=> console.log("val", val))

The executor function you pass to new Promise is executed immediately, before the new promise is returned. So when you do:
var p1 = new Promise(function(resolve, reject) {
setTimeout(() => resolve("first"), 5000);
});
...by the time the promise is assigned to p1, the setTimeout has already been called and scheduled the callback for five seconds later. That callback happens whether you listen for the resolution of the promise or not, and it happens whether you listen for resolution via the await keyword or the then method.
So your code starts three setTimeouts immediately, and then starts waiting for the first promise's resolution, and only then waiting for the second promise's resolution (it'll already be resolved, so that's almost immediate), and then waiting for the third (same again).
To have your code execute those setTimeout calls only sequentially when the previous timeout has completed, you have to not create the new promise until the previous promise resolves (using shorter timeouts to avoid lots of waiting):
console.log("starting");
new Promise(function(resolve, reject) {
setTimeout(() => resolve("first"), 1000);
})
.then(result => {
console.log("(1) got " + result);
return new Promise(function(resolve, reject) {
setTimeout(() => resolve("second"), 500);
});
})
.then(result => {
console.log("(2) got " + result);
return new Promise(function(resolve, reject) {
setTimeout(() => resolve("third"), 100);
});
})
.then(result => {
console.log("(3) got " + result);
console.log("last to print");
});
Remember that a promise doesn't do anything, and doesn't change the nature of the code in the promise executor. All a promise does is provide a means of observing the result of something (with really handy combinable semantics).
Let's factor out the common parts of those three promises into a function:
function delay(ms, ...args) {
return new Promise(resolve => {
setTimeout(resolve, ms, ...args);
});
}
Then the code becomes a bit clearer:
function delay(ms, ...args) {
return new Promise(resolve => {
setTimeout(resolve, ms, ...args);
});
}
console.log("starting");
delay(1000, "first")
.then(result => {
console.log("(1) got " + result);
return delay(500, "second");
})
.then(result => {
console.log("(2) got " + result);
return delay(100, "third");
})
.then(result => {
console.log("(3) got " + result);
console.log("last to print");
});
Now, let's put that in an async function and use await:
function delay(ms, ...args) {
return new Promise(resolve => {
setTimeout(resolve, ms, ...args);
});
}
(async() => {
console.log("starting");
console.log("(1) got " + await delay(1000, "first"));
console.log("(2) got " + await delay(500, "second"));
console.log("(3) got " + await delay(100, "third"));
console.log("last to print");
})();
Promises make that syntax possible, by standardizing how we observe asynchronous processes.
Re your edit:
1: if executor function passed to new Promise is executed immediately, before the new promise is returned, then why are here promises resolved ()synchronously) first and after the setTimeouts (asynchronously) gets executed?
There are two parts to that question:
A) "...why are here promises resolved ()synchronously) first..."
B) "...why are here promises resolved...after the setTimeouts (asynchronously) gets executed"
The answer to (A) is: Although you resolve them synchronously, then always calls its callback asynchronously. It's one of the guarantees promises provide. You're resolving p1 (in that edit) before the executor function returns. But the way you're observing the resolutions ensures that you observe the resolutions in order, because you don't start observing p2 until p1 has resolved, and then you don't start observing p3 until p2 is resolved.
The answer to (B) is: They don't, you're resolving them synchronously, and then observing those resolutions asynchronously, and since they're already resolved that happens very quickly; later, the timer callbacks run. Let's look at how you create p1 in that edit:
var p1 = new Promise(function (resolve, reject) {
setTimeout(() => console.log("first"), 5000);
resolve("first resolved")
});
What happens there is:
new Promise gets called
It calls the executor function
The executor function calls setTimeout to schedule a callback
You immediately resolve the promise with "first resolved"
new Promise returns and the resolved promise is assigned to p1
Later, the timeout occurs and you output "first" to the console
Then later you do:
p1.then((val) => {
console.log("(1)", val)
return p2
})
// ...
Since then always calls its callback asynchronously, that happens asynchronously — but very soon, because the promise is already resolved.
So when you run that code, you see all three promises resolve before the first setTimeout callback occurs — because the promises aren't waiting for the setTimeout callback to occur.
You may be wondering why you see your final then callback run before you see "third" in the console, since both the promise resolutions and the console.log("third") are happening asynchronously but very soon (since it's a setTimeout(..., 0) and the promises are all pre-resolved): The answer is that promise resolutions are microtasks and setTimeout calls are macrotasks (or just "tasks"). All of the microtasks a task schedules are run as soon as that task finishes (and any microtasks that they schedule are then executed as well), before the next task is taken from the task queue. So the task running your script does this:
Schedules a task for the setTimeout callback
Schedules a microtask to call p1's then callback
When the task ends, its microtasks are processed:
The first then handler is run, scheduling a microtask to run the second then handler
The second then handler runs and schedules a micro task to call the third then handler
Etc. until all the then handlers have run
The next task is picked up from the task queue. It's probably the setTimeout callback for p3, so it gets run and "third" appears in the console
Return value vs. resolve promise:
The part you've put in the question doesn't make sense to me, but your comment on this does:
I read that returning a value or resolving a promise is same...
What you've probably read is that returning a value from then or catch is the same as returning a resolved promise from then or catch. That's because then and catch create and return new promises when they're called, and if their callbacks return a simple (non-promise) value, they resolve the promise they create with that value; if the callback returns a promise, they resolve or reject the promise they created based on whether that promise resolves or rejects.
So for instance:
.then(() => {
return 42;
})
and
.then(() => {
return new Promise(resolve => resolve(42));
})
have the same end result (but the second one is less efficient).
Within a then or catch callback:
Returning a non-promise resolves the promise then/catch created with that value
Throwing an error (throw ...) rejects that promise with the value you throw
Returning a promise makes then/catch's promise resolve or reject based on the promise the callback returns

You cannot make asynchronous code execute synchronously.
Even async / await are just syntax that gives you a synchronous-style control flow inside a promise.
When I try to chain my promises, however, nothing happens except for the console.log of "last to be printed". Any insight would be great!
The other functions don't generate any output. That has nothing to do with them being in promises.
You start three timers (all at the same time), then log 'last to print', then chain some promises so that 'last to be printed' will print when all three promises resolve (5 seconds after you start them all going).
If you want the timers to run sequentially, then you have to initiate them only when the previous one has finished, and if you want to see what they resolve with then you have to write code that actually looks at that.
function p1() {
return new Promise(function(resolve, reject) {
setTimeout(() => resolve("first"), 5000);
});
}
function p2() {
return new Promise(function(resolve, reject) {
setTimeout(() => resolve("second"), 2000);
});
}
function p3() {
return new Promise(function(resolve, reject) {
setTimeout(() => resolve("third"), 1000);
});
}
function log(value) {
console.log("Previous promise resolved with " + value);
}
p1()
.then(log)
.then(p2)
.then(log)
.then(p3)
.then(log)
.then(() => console.log("last to be printed"));
Async/await is, arguably, neater:
function p1() {
return new Promise(function(resolve, reject) {
setTimeout(() => resolve("first"), 5000);
});
}
function p2() {
return new Promise(function(resolve, reject) {
setTimeout(() => resolve("second"), 2000);
});
}
function p3() {
return new Promise(function(resolve, reject) {
setTimeout(() => resolve("third"), 1000);
});
}
function log(value) {
console.log("Previous promise resolved with " + value);
}
(async function() {
log(await p1());
log(await p2());
log(await p3());
console.log("last to be printed");
}());

If you need to call an await but the function that contains that await doesn't have to be async, because you need, for example, a "number" and not a "Promise number ", you can do de next:
var ex: number = new Number(async resolve => {
var f = await funcionExample();
resolve(f);
}).valueOf();

The batch function passed to the ".run" method didn't return a promise

Although I do realize what the error means and why it happens, I think I have a use case that goes outside the expected. I am using Word.run() inside another promise, like so:
return new Promise((resolve, reject) => {
window.Word.run(context => {
// do stuff with context
resolve(someData);
});
});
So, if I understood it correctly, this resolves my promise, but leaves the .run method hanging since there's no return context.sync() at the end? Or did I get it wrong? If I'm right, how can I rewrite the example above to keep .run working properly?

If you want your promise to resolve after the context syncs...
return new Promise((resolve, reject) => {
window.Word.run(context => {
// do stuff with context
return context.sync().then(function() {
resolve(someData); // promise will resolve after sync resolves
});
});
});
If you don't need to resolve after but just want to sync the context at some point in the future, you can actually do this and it won't wait for the sync:
return new Promise((resolve, reject) => {
window.Word.run(context => {
// do stuff with context
resolve(someData); // this will resolve the promise
return context.sync(); // this will actually still happen since the function never returns
});
});

Extra promise at start and Extra promise at end

New at promises, so feel free to be verbose.
I am writing a function "extra_promises_at_start_and_end" that returns a promise to do something.
This function may know immediately that it will fail (ie: return a promise that is rejected). Question 1: Is there something like Promise.give_me_a_rejected_promise(..) or do I have to create a promise and reject it just like my code does?
Similarly, my function "extra_promises_at_start_and_end" calls other functions that return promises. At the end of this async chaining of work, I need to some final processing. Question 2a/2b: Since my function returns a promise, I need to create a promise to do this last bit of work. Is this correct that I need to create a promise and immediately accepted or reject it? Is there a Promise.give_me_a_rejected_promise(..).
My code works as expected, just feels like I am missing something, and so generating redundant code.
Code in question:
// this is the function that may have redundant code
// see question 1 and 2
function extra_promises_at_start_and_end() {
// fake out some module scope variable that indicates if this call is allowed to proceed or not
let ok_to_proceed = Math.random() > 0.5
// this function "extra_promises_at_start_and_end returns" a promise,
// Question 1: I need to create a Promise just to reject it immediatly?
if (!ok_to_proceed) {
return new Promise((resolve, reject) => { reject("failed before starting anything") }) // feels wrong
}
// do 5 things in sequence
return another_module_promise_to_do_something(1).then(() => {
return another_module_promise_to_do_something(2)
}).then(() => {
return another_module_promise_to_do_something(3)
}).then(() => {
return another_module_promise_to_do_something(4)
}).then(() => {
return another_module_promise_to_do_something(5)
}).then(() => {
// need to do something after the above 5 tasks are done,
console.log("doing something after all 5 things are done")
// this function "extra_promises_at_start_and_end" returns a promise,
// Question 2a: I need to create a promise just to resolve it immediatly?
return new Promise((resolve, reject) => { resolve(); }) // feels wrong
}).catch((id) => {
// this function extra_promises_at_start_and_end returns a promise,
// Question 2b: I need to create one just to reject it immediatly?
return new Promise((resolve, reject) => { reject(id); }) // feels wrong
})
}
The caller of this code is expecting a promise.
// run the test
console.log("calling something that will return a promise to let me know when it's done");
extra_promises_at_start_and_end()
.then(() => {
console.log("done :)")
}).catch((id) => { console.log("failed id = " + id) })
Finally, a stub for testing my function
// pretend this is a complex task (ie: not suitable for inlining)
// done by some other module
// it returns a promise
function another_module_promise_to_do_something(id) {
console.log("starting " + id)
let P = new Promise((resolve, reject) => {
console.log(" inside promise " + id)
setTimeout(() => {
if (Math.random() > 0.1) {
console.log(" finished " + id);
resolve();
} else {
console.log(" failed " + id)
reject(id);
}
}, Math.random() * 1000)
})
return P;
}
If this is the way it is supposed to be done, then let me know and I will stop searching for the correct way to use promises.

What I learned is:
Promise.resolve(value) method returns a Promise object that is resolved with the given value. So anyone calling my function can do a then on the response.
Promise.reject(reason) method returns a Promise object that is rejected with the given reason. So any chaining will fail as needed.
Any return value in then will get encapsulated in a promise. Feels like this obscures the intent. So not using.
My new function is as follows:
function promise_something() {
// fake out some module scope variable that indicates if this call is allowed to proceed or not
let ok_to_proceed = Math.random() > 0.5
if (!ok_to_proceed) {
return Promise.reject("failed before starting anything")
}
// do 5 things in sequence
return another_module_promise_to_do_something(1).then(() => {
return another_module_promise_to_do_something(2)
}).then(() => {
return another_module_promise_to_do_something(3)
}).then(() => {
return another_module_promise_to_do_something(4)
}).then(() => {
return another_module_promise_to_do_something(5)
}).then(() => {
// need to do something after the above 5 tasks are done,
console.log("doing something after all 5 things are done")
return Promise.resolve()
}

The then() and catch() functions of a Promise return a Promise.
Your last big chunk of code is indeed redundant. If you needed to do any processing after the 5th chained invocation of then(), you could just chain another then().
Here's a more bare-bones version of your code to illustrate:
const countFromOneToFive = () => {
if (Math.random() > 0.5) {
return Promise.reject("Cosmic radiation ruined your promises. Great.");
}
return Promise.resolve([])
.then((countToFive) => {
countToFive.push(1);
return countToFive;
})
.then((countToFive) => {
countToFive.push(2);
return countToFive;
})
.then((countToFive) => {
countToFive.push(3);
return countToFive;
})
.then((countToFive) => {
countToFive.push(4);
return countToFive;
})
.then((countToFive) => {
countToFive.push(5);
return countToFive;
});
};
countFromOneToFive()
.then((countToFive) => {
countToFive.forEach((number) => console.log(number));
})
.catch((error) => {
console.log(error, "Curses!");
});
You can use Promise.reject() to just return a rejected Promise. This is handled in the catch statement in the bottom.
You can do all of your processing with as many then() invocations as you want. You can simply return after your final then() to have a Promise. From there, treat it like any promise and append then()s and catch()s as you see fit.

1: Is there something like Promise.give_me_a_rejected_promise(..) or do I have to create a promise and reject it just like my code does?
like Promise.reject(err)?
// Question 2a: I need to create a promise just to resolve it immediatly?
The point where this is written in your code is inside a promise chain. You don't need to do anything at all (in that context), to return a resolved Promise, except maybe not throwing.
This Promise will resolve to any value you return, except undefined. And if you return undefined (explicitely or implicitely), this Promise will resolve to the last value before that, in the Promise chain.
Only if you need to explicitely resolve to undefined you'd have to return Promise.resolve().
// Question 2b: I need to create one just to reject it immediatly?
Still inside the Promise chain: Since a rejected value is like a thrown Error in sync code, all you need to do here is to throw.
But that is pointless in the context you asked. Why catching an Error, just to immediately throw the very same Error, without doing anything else in that catch-block.
So your code could be like
function extra_promises_at_start_and_end() {
// fake out some module scope variable that indicates if this call is allowed to proceed or not
let ok_to_proceed = Math.random() > 0.5
if (!ok_to_proceed) {
return Promise.reject("failed before starting anything");
}
// do 5 things in sequence
return another_module_promise_to_do_something(1)
.then(() => another_module_promise_to_do_something(2))
.then(() => another_module_promise_to_do_something(3))
.then(() => another_module_promise_to_do_something(4))
.then(() => another_module_promise_to_do_something(5))
.then(() => {
// need to do something after the above 5 tasks are done,
console.log("doing something after all 5 things are done")
return null; //so the previous value is no longer propagated by this Promise
})
//.catch(id => { throw id }) //is pointless.
}
When you say "This Promise will resolve to any value you return". So returning new Promise((resolve, reject) => { resolve 100}).then .... blaw blaw blaw is the same as 100.then .. blaw blaw blaw ?
Not exactly. Inside a Promise chain, returning a plain value like 100 or a Promise that resolves to 100 (like return Promise.resolve(100)) is equivalent in result ...
var foo1 = somePromise.then(() => {
//do something
return 100
})
//is equivalent in result to
var foo2 = somePromise.then(() => {
//do something
return Promise.resolve(100);
})
//or to
var foo3 = somePromise.then(() => {
//do something
return new Promise(resolve => resolve(100));
})
foo1, foo2, foo3 are all promises that resolve to the value 100 after somePromise has finished. That's equivalent in result.
... but you can't call then() on a number.
//you can do
somePromise.then(() => {
//do something
return 100
}).then(...)
//or sometimes you want to do
somePromise.then((value) => {
//usually because you need `value` inside `.then(...)`
return somethingAsync().then(...)
})
//but you can NOT do
somePromise.then(() => {
//do something
return 100.then(...)
})

Using await within a Promise

There seems something inherently wrong with having to define a Promise's callback as asynchronous:
return new Promise(async (resolve, reject) => {
const value = await somethingAsynchronous();
if (value === something) {
return resolve('It worked!');
} else {
return reject('Nope. Try again.');
}
});
This is apparently an antipattern and there are coding problems which can arise from it. I understand that it becomes easier to fail to catch errors here, even when placing await statements inside try/catch blocks.
My first question is, what's the best way to code something like this, when one wants to forward a Promise with different resolve/reject values? With then/catch? I.e.
return new Promise((resolve, reject) => {
somethingAsynchronous().then(value => {
if (value === something) {
return resolve('It worked!');
} else {
return reject('Nope. Try again.');
}
}); // errors would now be propagated up
});
Or do you just take it out the Promise constructor altogether as suggested here?
async function outerFunction() {
const value = await somethingAsynchronous();
return new Promise((resolve, reject) => {
if (value === something) {
return resolve('It worked!');
} else {
return reject('Nope. Try again.');
}
});
}
But what if you have several await statements in the outerFunction(), i.e. a linear code block calling several asynchronous functions. Would you then have to create and return a new Promise every time?
But then how do you account for code such as this?
async function outerFunction() {
if (someSynchronousCheck()) {
return 'Nope. Try again.' // another reject case
}
const value = await somethingAsynchronous();
// ...
}
I have the feeling that I'm making this more complicated than it should be. I'm trying to avoid nesting callbacks/chaining then/catch blocks without creating more problems in the future.
My final question is, why is the callback passed to a Promise not inherently async? It is already wrapped within a promise and expects the resolve/reject functions to be called asynchronously.

You do this:
async function outerFunction() {
const value = await somethingAsynchronous();
if (value === something) {
return 'It Worked!';
}
throw Error('Nope. Try again.');
}
Using async wraps the result of outerFunction with a Promise.
If you want that wrapping promise to resolve to something, just return it from the async function. If you want the wrapping promise to be rejected, throw an error inside the async function.
But then how do you account for code such as this?
async function outerFunction() {
if (someSynchronousCheck()) {
throw Error('Nope. Try again.');
}
const value = await somethingAsynchronous();
// ...
}

new Promise(async (resolve, reject) => { ... }) is relatively new antipattern. It results in creating 2 promise objects instead of 1, uncaught errors that happen inside constructor cannot be caught with try..catch and result in unhandled rejection.
Considering that promise asynchronous code can be handled with async..await, current use case for Promise constructor is non-promise asynchronous code, e.g.:
new Promise(resolve => setTimeout(resolve, 1000))
When Promise constructor contains synchronous code or involves other promises, a promise should be constructed with async function. A drop-in replacement is async IIFE:
return (async (resolve, reject) => {
const value = await somethingAsynchronous();
if (value === something) {
return 'It worked!';
} else {
throw 'Nope. Try again.';
}
})();
If the need for Promise constructor still presents when being used together with async, Promise constructor should be moved down in hierarchy so it won't wrap any async function.
My final question is, why is the callback passed to a Promise not inherently async? It is already wrapped within a promise and expects the resolve/reject functions to be called asynchronously.
async function isn't just a function that is executed asynchronously, it returns another promise that is supposed to be utilized - or at least handled with catch. Promise isn't supposed to utilize a promise that is returned from constructing function.
The constructor can resolve on same tick and doesn't necessarily have to be asynchronous.
Promise.resolve(1);
is similar to
Promise(resolve => resolve(1))
and not to
Promise(resolve => setTimeout(() => resolve(1)))

You can also chain the promises yourself by simply doing this:
return new Promise((resolve, reject) => {
somethingAsynchronous().then((value) => {
if (value === something) {
return resolve('It worked!');
} else {
return reject('Nope. Try again.');
}
}, (error) => { reject(error); });
});
I've been using this for some time and it works perfectly for me.

JS ES6 Promise Chaining

I'm trying to learn how to use promises, but am having trouble comprehending the chaining. I assume that with this code, both promises will run. Then when I call test.then() it should know that test has resolved and pass the resolve data to then().
Once that function finishes, it goes onto the next then(), repeating the same process with the test2 promise.
However, I can only get it to print out the first promise results, not the second. Any ideas what is missing here?
var test = new Promise(function(resolve, reject){
resolve('done1');
});
var test2 = new Promise(function(resolve, reject){
resolve('done2');
});
test
.then(function(data) {
console.log(data);
})
.then(test2)
.then(function(data) {
console.log(data);
});

Your first .then call is returning undefined, whereas any subsequent .then is expecting a returned promise. So you'd need to change your code to:
var test = new Promise(function(resolve, reject){
resolve('done1');
});
var test2 = new Promise(function(resolve, reject){
resolve('done2');
});
test
.then(function(data) {
console.log(data);
return test2;
})
.then(resultOfTest2 => doSomething)
.then(function(data) {
console.log(data);
});

You need to return next promise from the then callback:
test.then(function(data) {
console.log(data);
return test2;
}).then(function(data) {
console.log(data);
});

Summary:
The basic concept of promise chaining with promises is that every then / catch method on a fulfilled promise returns another promise. It works in the following manner:
When a promise is resolved the callback passed in the then method is called. The then method wraps the value which is returned in its callback in a resolved promise and returns this resolved promise.
When a promise is rejected the callback passed in the catch method is called. The catch method wraps the value which is returned in its callback in a rejected promise and returns this rejected promise.
Example:
Before fully understanding the concept of chaining multiple then methods it is important to know what exactly the return values of then and catch are. Take the following example:
let prom1 = new Promise((res, rej) => {
res('res');
});
const resolvedProm1 = prom1.then((val) => {return val});
// setTimeout needed for the promise to actually be resolved
setTimeout(() => console.log(resolvedProm1));
let prom2 = new Promise((res, rej) => {
rej('rej');
});
const resolvedProm2 = prom2.catch((err) => {throw err});
// setTimeout needed for the promise to actually be rejected
setTimeout(() => console.log(resolvedProm2));
We can observe the status of the promises in the chrome devtools:
What basically happens is that in a then or catch callback is the following:
Any value returned in a then or catch callback is wrapped in Promise.resolve() and a new resolved promise is returned.
Any error thrown in a then or catch callback is wrapped in Promise.reject() and a new rejected promise is returned.
Because we are getting returned a rejected or resolved promise object we can repeat the cycle and call the then or catch method on it again. For example:
const prom = new Promise((res, rej) => {
if (Math.random() > 0.5) {
res('success');
} else {
rej('error');
}
});
prom.then((val) => {
return val;
}).then((val) => {
return val
}).then((val) => {
console.log(val)
}).catch((err) => {
console.log('err');
})
This calling of then and catch methods which are executed in their respective order is called promise chaining. It is a very useful technique to make working with asynchronous code easier, especially if multiple asynchronous operations need to be performed which are dependend on each others data.

you need to return the other promise(test2) in the first promise (test1) to allow for chaining:
var test = new Promise(function(resolve, reject){
resolve('done1');
});
var test2 = new Promise(function(resolve, reject){
resolve('done2');
});
test
.then(function(data) {
console.log(data);
return test2;
});

You may also want to try -
let test = new Promise(function(resolve, reject){
resolve('done1');
});
let test2 = new Promise(function(resolve, reject){
resolve('done2');
});
try {
let logOne = test();
let logTwo = test2();
console.log(logOne);
console.log(logTwo);
} catch(error) {
console.error(error);
}
In this way, you can also properly handle any promise dependencies. For example if test one relied on test two's data your could -
try {
let logOne = test();
let logTwo = test2(logOne);
console.log(logOne);
console.log(logTwo);
} catch(error) {
console.error(error);
}