how can make synchronous promise in angular2 - http

Question

I am trying to call a function located in service class,and if that function returns data,one boolean variable sets true. I have 2 class as bollow:student.ts and service.ts:
// student.ts
public ngOnInit() {
this.config.load().then(() => {
this.service.getRecords().then(
function () { console.log("success getRecord");
this.loading = false; },
function () { console.log("failed getRecord");
this.loading = true; });
});
}
//service.ts
public getRecord(id: number): Promise<T> {
return this.getRecordImpl();
}
private getRecordsImpl(): Promise<T[]> {
let url = this.serviceUrl;
return this.http.get(url, this.getRequestOptionsWithToken())
.toPromise()
.then(res => {
this.records = this.extractData<T[]>(res);
for (var i = 0; i < this.records.length; i++) {
var record = this.records[i];
this.onRecord(record);
}
return this.records;
})
.catch(this.handleError);
}
by the now, records from service returns, but this.service.getRecords(); is undefined. and I can't use
.then
for handling succeed and failure actions.
I know that it is not good idea to make it synchronous. but think that being Asynchronous causes getRecords becomes undefined. What is the solution for handling that. I want it runs sequentially. and if service returns any records , variable initialize to false, otherwise it sets to true.
Many thanks for any help and guide.

Answer 1

I think your aproach is not correct, what is the point to make a promise synchronous ? If you really really want to do this I suggest you to dig in the Synchronous programming with es6 generators but usually the job is done much smother.
From your code I see that you are consuming your Promise by attaching .then() in the service. In this way you should create a new Promise.
private getRecordsImpl(): Promise<T[]> {
let url = this.serviceUrl;
return new Promise((resolve, reject) => {
this.http.get(url, this.getRequestOptionsWithToken())
.toPromise()
.then(res => {
this.records = this.extractData<T[]>(res);
for (var i = 0; i < this.records.length; i++) {
var record = this.records[i];
this.onRecord(record);
}
resolve(this.records);
})
.catch(this.handleError);
})
}
And in your code use:
this.service.getRecords().then(
function (records) { console.log("success getRecord");
this.loading = false; },
function (err) { console.log("failed getRecord");
this.loading = true; });