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How to synchronise my code execution in angular

I'm performing multiple task and each task is dependent on previous task execution. So in my example what I want is after getting all the Id, i should get their respective blob value and then finish the execution by storing it in a variable. I'm very new to javascript and angular, please help me out. Here's what I'm trying
//this method will get the response from the rest api
async getIDFromAssets(){
this.blobDataArray=[];
this.service.getAssetsData().subscribe(async (res: JSON) => {
//after getting the response I'm filtering through it to get sepcific Id using this.getFileId() method
this.getFileId(res).then((data)=>{
console.log("blob "+data)
})
})
}
//below method will get one Id at a time and will call another method to get it's blob value
async getFileId(res){
this.fileId = [];
Object.keys(res).forEach(keys => {
if (keys == 'emb') {
let responseValue = res[keys];
Object.keys(responseValue).forEach(async (keys1) => {
if (keys1 === 'file') {
let responseArray = responseValue[keys1];
for (let file of responseArray) {
let temp: string = file.metadata.contentType;
if (temp.startsWith('image')) {
//Here I'm getting id value 'file._id' and using that I'm calling another method 'getBlobData()' to get its blob value
let data=await this.getBlobData(file._id);
this.blobDataArray.push(data);
}
}
return this.blobDataArray
}
});
}
});
}
// method to get the blob value
async getBlobData(fileId){
this.articleDetailService.getBlobDataFromAssets(fileId).subscribe(async (res)=>{
let imageObj={
'id':fileId,
'blob':res
}
return imageObj;
})
}

You need to use RxJs to avoid the nested subscription to chain your calls, possible methods to use are mergeMap and filter
Please take a look at this answer here.

Dynamically get data from firebase realtime database during runtime in javascript

I have the following problem: I want to get data from a specific node from firebase during runtime. It should display "stats" of a player that was selected before. Now I could use on() to get all the data in the beginning, but I want to save data transfers by only downloading the data of on player if I need to, so I tried to use once like this:
var firebaseRef = firebase.database().ref();
function getScoresOfPlayer(player) {
console.log(player);
var selectedPlayerScores = [];
firebaseRef.once('value').then(function(snap) {
snap.child('scores').child('thierschi').forEach(function(child) {
selectedPlayerScores.push([child.key, child.val()]);
});
});
return selectedPlayerScores;
}
The problem is that it retruns the array before the data was loaded into it. Also I checked the docs and didn't find a better solution.
Thanks in advance!

This is because the getScoresOfPlayer function returns selectedPlayerScores before the promise returned by the once() method resolves.
You should include the return within the then(), as follows:
var firebaseRef = firebase.database().ref();
function getScoresOfPlayer(player) {
console.log(player);
var selectedPlayerScores = [];
return firebaseRef.once('value') //return here as well
.then(function(snap) {
snap.child('scores').child(player).forEach(function(child) { //I guess it should be child(player) and not child('thierschi') here
selectedPlayerScores.push([child.key, child.val()]);
});
return selectedPlayerScores;
});
}
which means that you have to call your function as follows, since it is going to be asynchronous and to return a promise:
getScoresOfPlayer('xyz')
.then(function(selectedPlayerScores) {
....
})

How to dynamically create and populate multiple objectStores on HTML5 IndexedDB in the same transaction?

Working on the IndexedDB API, I'm creating many objectStores that belong to the same database, in one transaction, when the user loads a webpage.
I order to do so, I created an object which contains many objectStores to be created, each one has it's name, data and index.
Then a function runs the object and effectively creates Database, objectStores and indexes for each one.
However of all OS's created, just the last member of the object gets populated. Say of 5 objects to be created and populated, 5 are created but only the last one is populated.
Clearly is a problem of overwriting or some issue related to the JS stack or asynchronicity.
I appreciate any help to make the code populate all OS not the last one.
My browser is Chrome 56, I fetch data from an API whose response is OK, and I'm coding on vanillajs. I appreciate your help in vanillajs, there is no way to use any library or framework different from what the modern Web Platform offers.
Here is the code:
On the HTML side, this is an example of the object:
var datastores = [{osName:'items', osEndpoint: '/api/data/os/1/1', osIndex:'value'}, {osName:'categories', osEndpoint: '/api/data/os/2/1', osIndex: 'idc'}];
On javascript:
var request = indexedDB.open(DB_NAME, DB_VERSION); // open database.
request.onerror = function (e) { // error callback
console.error("error: " + e.target.errorCode);
};
request.onupgradeneeded = function (e) { // the onupgradeneeded event which creates all schema, dataabase, objectstores and populates OS.
var db = this.result;
for (var i in datastores) { // loop the objectStore object.
var objectStore = db.createObjectStore(datastores[i].osName, {keyPath: "id"});
TB_NAME = datastores[i].osName; // instantiate each objectStore name.
objectStore.createIndex(datastores[i].osIndex, datastores[i].osIndex, { unique: false }); // create each index.
objectStore.transaction.oncomplete = function(e) { // oncomplete event, after creating OS...
fetchGet(datastores[i].osEndpoint, popTable); // runs a function to fetch from a designated endpoint and calls a function.
};
}
}
Now the functions: to fetch data and to populate data:
function fetchGet(url, function) { // fetch from API.
fetch(url, {
method: 'GET'
}).then(function(response) {
return response.json();
}).then(function(json) {
popTable (json);
}).catch(function(err) {
console.log('error!', err);
});
}
function popTable(json) {
var m = 0;
var tx = db.transaction(TB_NAME, "readwrite");
tx.oncomplete = function(e) {
console.log("Completed Transaction " + TB_NAME);
};
tx.onerror = function(e) {
console.error("error: " + e.target.errorCode);
};
var txObjectStore = tx.objectStore(TB_NAME);
for (m in json) {
var request = txObjectStore.add(json[m]);
request.onsuccess = function (e) {
console.log('adding... ' );
};
}
}

The for (var i in datastores) loop runs synchronously, updating the global TB_NAME variable every time. When the loop finishes, TB_NAME will be holding the name of the last object store.
By the time the asynchronous popTable calls run, TB_NAME will forever be holding the name of the last store, so that's the only one that will update. Try adding logging to popTable to see this.
You'll need to pass the current value of the store name along somehow (e.g. as an argument to fetchGet). Also note that although you pass popTable as a parameter when calling fetchGet you're not actually accepting it as an argument.
...
Specific changes:
Change how you call fetchGet to include the store name:
fetchGet(datastores[i].osEndpoint, popTable, datastores[i].osName);
Change the fetchGet function to accept the args:
function fetchGet(url, func, name) {
And then instead of calling popTable directly, do:
func(json, name);
And then change the definition of popTable to be:
function popTable(json, name) {
... and use name in the transaction.

accessing object values that are inside an array

I'm hoping someone can help with what is likely a simple answer - but I'm ready to bash my head against the wall....again.
I have a function which makes a JSON call to an API, and then pushes the results into an array. The function appears to work just fine as my console.log is showing that the array is populated correctly.
I'm struggling with how to access the values of the modified twichResult object (after the function has run), so that I can do 'stuff' with it. e.g. display the value of the 'status' property onscreen etc... I give some examples of what I've tried in the in the large commented out section.
I'd really appreciate some intelligence weighing in on this as I've exhausted my resources. Thanks in advance.
<script type="text/javascript">
$(document).ready(function() {
var twitchResult = {results:[]};
var channel = { logo:"", display_name:"", status:"", url:"" };
var finalUrl = "https://api.twitch.tv/kraken/streams/freecodecamp?callback=?"
getTwitchers (finalUrl, "freecodecamp");
console.log(twitchResult);
// How do I access the individual values in the object TwitchResult?
// I get "undefined" in the console if I try to access the object's property values
// I've tried every way I can think of to get 'into' the returned object :
// console.log(twitchResult.results);
// console.log(twitchResult["results"])
// console.log(twitchResult.results.status)
// console.log(twitchResult[0])
// console.log(twitchResult[0][0])
// etc etc
function getTwitchers (url, item) {
$.getJSON(url, function(data) {
var obj = data.stream;
// Check if the object is not valid using (obj == null) which is shorthand for both null and undefined
if (obj == null) {
if (obj === undefined) {
channel.display_name = item;
channel.status = "closed";
console.log ("this is undefined");
}
else {
channel.display_name = item;
channel.status = "offline";
console.log("this is null");
}
}
else {
channel.logo = obj.channel.logo;
channel.display_name = obj.channel.display_name;
channel.status = obj.channel.status;
channel.url = obj.channel.url;
console.log("valid entry");
}
twitchResult["results"].push(channel);
// twitchResult.results.push(channel);
// console.log(twitchResult);
});
}
});
</script>

$.getJSON is making an ajax-request. You must handle this request from within the request handler. When getTwichers returns, twichResults is not yet set.
There are methods to delay Program execution, until twichResults is done, but You should not think of using them, since they would delay program execution. The idea of ajax is to execute things asynchronously, without disturbing the rest of the execution flow. If the code You want to execute depends on the json, then You should add it to the handle in $.getJSON. Just write a new function (e.g. continue_execution(twichResult)) and invoke it right after twitchResult["results"].push(channel);. Just don't do anything after getTwitchers(...).
By the way: It is a good habit to define functions, before they are used, because it follows the flow the human eye reads the code and there are programming languages, which depend on this style of declaring function.
If this is unclear to You, then add a comment.

Casper JS waitForResource with a restful API

We are having a little problem with a functional test with casper.js.
We request the same resource twice, first with the GET and then with POST method.
Now when waiting for the second resource (POST) it matches the first resource and directly goes to the "then" function.
We would like to be able to check for the HTTP method in the "test" function, that way we can identify the resource properly. For now we use the status code (res.status), but that doesn't solve our problem fully, we really need the http method.
// create new email
this.click(xPath('//div[#id="tab-content"]//a[#class="button create"]'));
// GET
this.waitForResource('/some/resource',
function then() {
this.test.assertExists(xPath('//form[#id="email_edit_form"]'), 'Email edit form is there');
this.fill('form#email_edit_form', {
'email_entity[email]': 'test.bruce#im.com',
'email_entity[isMain]': 1
}, true);
// POST
this.waitForResource(
function test(res) {
return res.url.search('/some/resource') !== -1 && res.status === 201;
},
function then() {
this.test.assert(true, 'Email creation worked.');
},
function timeout() {
this.test.fail('Email creation did not work.');
}
);
},
function timeout() {
this.test.fail('Email adress creation form has not been loaded');
});
Or maybe there is a better way to test this scenario? Although since this is a functional test we need to keep all those steps in one test.

You can try to alter the form action url to add some query string, therefore generating a new resource appended to the stack. Could be done this way:
casper.thenEvaluate(function() {
var form = __utils__.findOne('#email_edit_form');
form.setAttribute('action', form.getAttribute('action') + '?plop');
});
That's a hack though, and functional testing should never be achieved that way. Let's hope more information will be added to the response objects in the future.

The res parameter that is passed to the test function has an ID. I created a helper that tests against this ID and blacklists it, so the same resource won't get accepted a second time.
var blackListedResourceIds = [],
testUniqueResource = function (resourceUrl, statusCode) {
return function (res) {
// check if resource was already loaded
var resourceFound = res.url.search(resourceUrl) !== -1;
// check statuscode
if (statusCode !== undefined) {
resourceFound = resourceFound && res.status === statusCode;
}
// check blacklisting
if (!resourceFound || blackListedResourceIds[res.id] !== undefined) {
return false;
} else {
blackListedResourceIds[res.id] = true;
return true;
}
};
};