Javascript Promise.all not show last

I have a few functions which return a promise.

There's a start function which executes another function.

As these are promises and I'm using Promise.all, in theory, Promise.all should show only after all the other promises are completed.

Promise.all

Here is the code:

arr = ;

function start() {
var aPromiseMain = new Promise((resolve, reject) => {
myfunction();
arr.push('start');
resolve(console.log('I am start'))
})
return aPromiseMain
}

start();

function myfunction() {
var aPromise = new Promise((resolve, reject) => {
setTimeout(() => {
arr.push('I am myfunction');
resolve(console.log('I am myfunction'))
}, 2000)
})
return aPromise
}

Promise.all(arr).then(values => {
console.log(values);
});


What's happening instead is the order is as follows:

myfunction

It should be:

myfunction

How can I fix this?

resolve()

Promise.all([1,2,3]).then(console.log)

4 Answers
4

From the author's description and comments, it looks like they might need to run the promises in series, so here is an alternative:

arr = ;

function start() {
console.log("I have started");
var aPromiseMain = new Promise((resolve, reject) => {
myfunction().then((result) => {
console.log('I am finished');
});
})
return aPromiseMain
}

function myfunction() {
var aPromise = new Promise((resolve, reject) => {
setTimeout(() => {
resolve(console.log('I am myfunction'))
}, 2000)
})
return aPromise
}

start();

Your array should be an array of promises, not an array of strings.

arr = ;

function start() {
var aPromiseMain = new Promise((resolve, reject) => {
resolve('I am start')
})
return aPromiseMain
}

function myfunction() {
var aPromise = new Promise((resolve, reject) => {
setTimeout(() => {
resolve('I am myfunction')
}, 2000)
})
return aPromise
}

arr.push(start());
arr.push(myfunction());

Promise.all(arr).then(values => {
console.log(values);
console.log("I am done");
});

myfunction()

start()

promise.all

a_promise.then()

Your code arr.push('start'); (for example) simply adds a string to the array. Promise.all needs access to the actual Promise objects, not strings. It cannot do anything useful with strings. Also sending the result of console.log as the value to the resolve functions makes no sense - the idea of this parameter is to give the listener some data back as a result - console.log logs things, but it doesn't return data.

arr.push('start');

console.log

resolve

This example pushes the Promise objects into the array so that Promise.all will wait for each to complete before executing, and also sends a meaningful response when the Promise resolves.

arr = ;


function start() {
var aPromiseMain = new Promise((resolve, reject) => {
console.log("start");
myfunction();
resolve('I am start');
});
arr.push(aPromiseMain);
return;
}

start();


function myfunction() {
var aPromise = new Promise((resolve, reject) => {
setTimeout(() => {
console.log("myfunction");
resolve('I am myfunction');
}, 2000)
})
arr.push(aPromise);
return;
}

Promise.all(arr).then(values => {
console.log(values);
});

function start() {
return new Promise((resolve, reject) => {
myfunction();
arr.push('start');
resolve(console.log('I am start'))
})
}
function myfunction() {
return new Promise((resolve, reject) => {
setTimeout(() => {
arr.push('I am myfunction');
resolve(console.log('I am myfunction'))
}, 2000)
})
}
var arr = [start(), myfunction()]
Promise.all(arr).then(values => {
console.log(values);
});


Try that way.

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