Passing values from one promise to the next [duplicate] - javascript

This question already has answers here:
How do I access previous promise results in a .then() chain?
(17 answers)
Closed 5 years ago.
A bit new to javascript.
Been dealing with promises, however ran into a problem i dont know how to approach.
How can i pass a value into the next promise resolve?
Here's my code
bot.on('ask.add_account_password', (msg) => {
let username = users[msg.from.id].username;
let password = msg.text;
var accounts = require('./inc/account.js');
accounts.login_account(username,password).then(function(data){
var account = data.params;
console.log(account);
return accounts.store(msg.from.id,username,password,account.followerCount);
}).then(function(data){
let caption = "Your account "+account.username+"("+account.fullName+")has been added\n";
return bot.sendPhoto(msg.from.id, account.picture, {caption:caption});
})
.catch(function(error){
console.log(error);
add_account(msg,error.name);
});
});
On the line where i create the caption variable, i'm trying to access the account object created in the block before it(var account = data.params) but i get a reference error saying its not defined. Now i can easily bypass this by just sending the entire object into the accounts.store function and have it resolve the object when done, but that just seems like a dirty workaround to a bigger problem. Is there a cleaner way to do this?

You can create variable (and set it in promise) in main function or you can return this as result of first promise instead of result from function store

account is undefined at second .then(), use data to reference the Promise value accounts.store returned from previous .then()
.then(function(data) {
// `data` : `accounts.store` returned from previous `.then()`
let caption = "Your account " + data.username
+ "(" + data.fullName + ")has been added\n";
return bot.sendPhoto(msg.from.id, data.picture, {caption:caption});
})

You can pass it in an array and use destructuring in the arguments to unpack the array.
accounts.login_account(username,password).then(function(data){
var account = data.params;
console.log(account);
return [account, accounts.store(msg.from.id,username,password,account.followerCount)];
}).then(function([account, data]){
let caption = "Your account "+account.username+"("+account.fullName+")has been added\n";
return bot.sendPhoto(msg.from.id, account.picture, {caption:caption});
})
You don't actually appear to be using data, so you could just return account after calling store

Related

Unable to add async / await and then unable to export variable. Any help appreciated

Background: Been trying for the last 2 day to resolve this myself by looking at various examples from both this website and others and I'm still not getting it. Whenever I try adding callbacks or async/await I'm getting no where. I know this is where my problem is but I can't resolve it myself.
I'm not from a programming background :( Im sure its a quick fix for the average programmer, I am well below that level.
When I console.log(final) within the 'ready' block it works as it should, when I escape that block the output is 'undefined' if console.log(final) -or- Get req/server info, if I use console.log(ready)
const request = require('request');
const ready =
// I know 'request' is deprecated, but given my struggle with async/await (+ callbacks) in general, when I tried switching to axios I found it more confusing.
request({url: 'https://www.website.com', json: true}, function(err, res, returnedData) {
if (err) {
throw err;
}
var filter = returnedData.result.map(entry => entry.instrument_name);
var str = filter.toString();
var addToStr = str.split(",").map(function(a) { return `"trades.` + a + `.raw", `; }).join("");
var neater = addToStr.substr(0, addToStr.length-2);
var final = "[" + neater + "]";
// * * * Below works here but not outside this block* * *
// console.log(final);
});
// console.log(final);
// returns 'final is not defined'
console.log(ready);
// returns server info of GET req endpoint. This is as it is returning before actually returning the data. Not done as async.
module.exports = ready;
Below is an short example of the JSON that is returned by website.com. The actual call has 200+ 'result' objects.
What Im ultimately trying to achieve is
1) return all values of "instrument_name"
2) perform some manipulations (adding 'trades.' to the beginning of each value and '.raw' to the end of each value.
3) place these manipulations into an array.
["trades.BTC-26JUN20-8000-C.raw","trades.BTC-25SEP20-8000-C.raw"]
4) export/send this array to another file.
5) The array will be used as part of another request used in a websocket connection. The array cannot be hardcoded into this new request as the values of the array change daily.
{
"jsonrpc": "2.0",
"result": [
{
"kind": "option",
"is_active": true,
"instrument_name": "26JUN20-8000-C",
"expiration_timestamp": 1593158400000,
"creation_timestamp": 1575305837000,
"contract_size": 1,
},
{
"kind": "option",
"is_active": true,
"instrument_name": "25SEP20-8000-C",
"expiration_timestamp": 1601020800000,
"creation_timestamp": 1569484801000,
"contract_size": 1,
}
],
"usIn": 1591185090022084,
"usOut": 1591185090025382,
"usDiff": 3298,
"testnet": true
}
Looking your code we find two problems related to final and ready variables. The first one is that you're trying to console.log(final) out of its scope.
The second problem is that request doesn't immediately return the result of your API request. The reason is pretty simple, you're doing an asynchronous operation, and the result will only be returned by your callback. Your ready variable is just the reference to your request object.
I'm not sure about what is the context of your code and why you want to module.exports ready variable, but I suppose you want to export the result. If that's the case, I suggest you to return an async function which returns the response data instead of your request variable. This way you can control how to handle your response outside the module.
You can use the integrated fetch api instead of the deprecated request. I changed your code so that your component exports an asynchronous function called fetchData, which you can import somewhere and execute. It will return the result, updated with your logic:
module.exports = {
fetchData: async function fetchData() {
try {
const returnedData = await fetch({
url: "https://www.website.com/",
json: true
});
var ready = returnedData.result.map(entry => entry.instrument_name);
var str = filter.toString();
var addToStr = str
.split(",")
.map(function(a) {
return `"trades.` + a + `.raw", `;
})
.join("");
var neater = addToStr.substr(0, addToStr.length - 2);
return "[" + neater + "]";
} catch (error) {
console.error(error);
}
}
}
I hope this helps, otherwise please share more of your code. Much depends on where you want to display the fetched data. Also, how you take care of the loading and error states.
EDIT:
I can't get responses from this website, because you need an account as well as credentials for the api. Judging your code and your questions:
1) return all values of "instrument_name"
Your map function works:
var filter = returnedData.result.map(entry => entry.instrument_name);
2)perform some manipulations (adding 'trades.' to the beginning of each value and '.raw' to the end of each value.
3) place these manipulations into an array. ["trades.BTC-26JUN20-8000-C.raw","trades.BTC-25SEP20-8000-C.raw"]
This can be done using this function
const manipulatedData = filter.map(val => `trades.${val}.raw`);
You can now use manipulatedData in your next request. Being able to export this variable, depends on the component you use it in. To be honest, it sounds easier to me not to split this logic into two separate components - regarding the websocket -.

Getting data from nested .then function [duplicate]

This question already has answers here:
How do I return the response from an asynchronous call?
(41 answers)
Closed 4 years ago.
Long story short. I'm trying to learn javascript. And i've been googling for about 4 hours straight right now. And i cant find the answer to my current problem, so i'm assuming i'm looking at this the wrong way.
I'm trying to create a slackbot. The bot is connected, and can look for messages so that part is working.
I've (tried to)create(ed) a function that gets the userID of everynew message based on the name i set in. In my mind this function returns the userID, and that i can later down the code check if userID is in message.text, if it is do something.
I'm assuming it has something to do with that .then function. Can i even return data from that .then function? or can u just use that data inside of that function.
I have several return functions as i was trying to just return it from wherever u could.
function getuserid(botname){
var id = ''
var getbotid = bot.getUsers();
getbotid.then(function(value){
for(var i=0;i<value.members.length;i++){
if(value.members[i].name == botname){
id = value.members[i].id
console.log(id);//this logs what i want.
return id
}
} return id
})
return id
}
var botid = getuserid('jokester');
console.log(botid);
I'm not sure but in my experience, if you return getbotid() then actually you return a promise and you can use it .
function getuserid(botname){
var id = ''
//************Here I return getbotid
return bot.getUsers().then(function(value){
for(var i=0;i<value.members.length;i++){
if(value.members[i].name == botname){
id = value.members[i].id
console.log(id);//this logs what i want.
return id
}
} return id
})
return id
}
//Now you can use it
getuserid('jokester').then(id => console.log(botid));

Firebase functions - Counting children and updating an entry

I have been trying to use Firebase Functions to write a simple method, but I am unfamiliar with JS.
Below is the structure of my Realtime Database
-spots
---is_hidden: false
---likes
------like_id_1: true
---dislikes
------dislike_id_1: true
I am trying to write a simple method that does the following: Whenever an entry is added to dislikes, count the likes and the dislikes.
If the number of dislikes is larger than the number of ( likes + 5 ),
change the value of is_hidden to true
This is my attempt to solving the problem
exports.checkHiddenStatus = functions.database.ref('/spots/{spotid}').onWrite(
(change, context) => {
const collectionRef = change.after.ref;
const isHiddenRef = collectionRef.child('is_hidden');
const likesRef = collectionRef.child('likes');
const dislikesRef = collectionRef.child('dislikes');
if(isHiddenRef.before.val()) return;
let likeCount = likesRef.numChildren();
let dislikeCount = dislikesRef.numChildren();
let isHidden = false;
if( dislikeCount >= (likeCount + 5))
isHidden = true;
if(!isHidden) return;
// Return the promise from countRef.transaction() so our function
// waits for this async event to complete before it exits.
return isHiddenRef.transaction((current) => {
return isHidden;
}).then(() => {
return console.log('Counter updated.');
});
});
Sadly, because I have no experience with JS I keep getting stuck with error messages I don't understand. The most recent being
TypeError: Cannot read property 'val' of undefined
at exports.checkHiddenStatus.functions.database.ref.onWrite (/user_code/index.js:28:28)
Can somebody please help me write this function? Thank you!
It looks like you're trying to treat a database Reference object like a Change object. Change has before and after properties, but a reference does not.
If you have a database reference object, and you want the value of the database at that location, you need to query it with its once() method.
Read more about reading and writing data using the Admin SDK.

JavaScript setting public variable [duplicate]

This question already has answers here:
How do I return the response from an asynchronous call?
(41 answers)
Closed 5 years ago.
I have a question regarding setting 'public' variable in JavaScript. Here is my code:
var storeKey;
firebase.database().ref('stores').orderByChild('storeAddress').equalTo('Blk 167').once('value', function(snapshot) {
var storeData = snapshot.val();
if (storeData){
console.log('exists');
}else{
storeKey = firebase.database().ref('stores').push({
storeName : "store1",
storeAddress : "Blk 167"
}).getKey();
//console.log("STORE " + storeKey);
}
});
console.log("STORE " + storeKey);
I am checking if the address exists before adding new record into Firebase. However, if I put the console.log at the last line, I get undefined. It only returns a value if I print it out inside the else statement.
I wanted to separate the storeKey out before I need that data in other places and I don't want my code to be nested inside the else statement. Any idea how to achieve this?
Your function accepts a callback, the console.log is called before the callback, that's why its undefined One way to "solve" it is using promises. e.g.
const deferred = q.defer();
firebase.database().ref('stores').orderByChild('storeAddress').equalTo('Blk 167').once('value', function(snapshot) {
var storeData = snapshot.val();
if (storeData){
console.log('exists');
}else{
storeKey = firebase.database().ref('stores').push({
storeName : "store1",
storeAddress : "Blk 167"
}).getKey();
deferred.resolve(storeKey);
}
});
deferred.then(console.log)

Why is the array variable not saved after the dbs call - node js [duplicate]

This question already has answers here:
Why is my variable unaltered after I modify it inside of a function? - Asynchronous code reference
(7 answers)
Closed 6 years ago.
I have a schema which saves Cat information. I then want to create an array of all the cat_urls, however when I call the array outside of the dbs call, the array is empty
var cat_urls = [];
Cat.find(function (err, data) {
var stringify = JSON.stringify(data)
content = JSON.parse(stringify);
content.forEach(function (result) {
cat_urls.push(result.cat_url);
})
console.log(cat_urls, 'here')
})
console.log(cat_urls, 'here not working') // I want cat_urls to also be populated here
So Inside the Cat.find() call cat_urls has values like this:
[ 'www.hello.co.uk', 'www.testing.co.uk' ] 'here'
But outside cat_urls = []
I guess this is to do with the fact that node js does not run in a specific order, but how can I solve this issue?
I think it's working but your find function returns a promise that resolves asynchronously.
Try:
var cat_urls = [];
Cat.find(function (err, data) {
var stringify = JSON.stringify(data)
content = JSON.parse(stringify);
content.forEach(function (result) {
cat_urls.push(result.cat_url);
})
console.log(cat_urls, 'here')
}).then(function(){
// Promise has completed, now this console log will trigger only after the cat's names are pushed.
console.log(cat_urls);
})

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