Typescript: Delay code execution until a function has completed running

Question

Typescript: Delay code execution until a function has completed running

I've encountered an issue with my code that involves calling a function. Here is the snippet of code in question:

this.getAllOptions(questionID);
console.log("++++++++++++++++++++++++++++++++");
console.log(this.result);

The task of this function is straightforward - it invokes a service, which then returns an array of objects. What I specifically require from this returned data is just the "item.Content," formatted as a string. Below is the relevant code snippet:

result: string;
getAllOptions(question_ID){

    this.result = "";

    this._service.getOptionsQuestion(question_ID)
        .subscribe( data => {
            data.forEach(item => {
            console.log(item.Content);
            this.result += item.Content;
            });
        });
}

However, a problem arises where the lines of code after invoking the "getAllOptions()" function are executed prematurely. I am seeking a way for those subsequent lines to wait until the function has completed execution.

Is there a solution to accomplish this?

typescript

Answer 1

Answer №1

Patience is key when waiting for data to arrive. As soon as the getOptionsQuestion function finishes executing, the observable it generates has not yet received any data, so the callback provided to the subscribe method remains inactive.

There are various strategies one can employ to wait for the data. Personally, I find the async/await syntax in Typescript to be my favored choice as it enhances code readability:

import 'rxjs/add/operator/toPromise';
import 'rxjs/add/operator/map';
import * as rsx from 'rxjs'

class Test {
    // Declaration of a dummy service
    _service : {
        getOptionsQuestion(nr: number): rsx.Observable<Array<{Content : string }>>
    }

    result: string;
    async getAllOptions(question_ID: number){

        this.result = "";
		const data = await this._service.getOptionsQuestion(question_ID).toPromise()

        data.forEach(item => {
            console.log(item.Content);
            this.result += item.Content;
        });
    }
    async otherMethod (questionID : number){
        await this.getAllOptions(questionID);
        console.log("++++++++++++++++++++++++++++++++");
        console.log(this.result);
    }
}

Answer 2

Patience is key when waiting for data to arrive. As soon as the getOptionsQuestion function finishes executing, the observable it generates has not yet received any data, so the callback provided to the subscribe method remains inactive.

There are various strategies one can employ to wait for the data. Personally, I find the async/await syntax in Typescript to be my favored choice as it enhances code readability:

import 'rxjs/add/operator/toPromise';
import 'rxjs/add/operator/map';
import * as rsx from 'rxjs'

class Test {
    // Declaration of a dummy service
    _service : {
        getOptionsQuestion(nr: number): rsx.Observable<Array<{Content : string }>>
    }

    result: string;
    async getAllOptions(question_ID: number){

        this.result = "";
		const data = await this._service.getOptionsQuestion(question_ID).toPromise()

        data.forEach(item => {
            console.log(item.Content);
            this.result += item.Content;
        });
    }
    async otherMethod (questionID : number){
        await this.getAllOptions(questionID);
        console.log("++++++++++++++++++++++++++++++++");
        console.log(this.result);
    }
}

Answer 3

Answer №2

To solve the problem, one approach is to utilize a promise in the getAllOptions function.

result: string;

getAllOptions(question_ID): Promise<void>{
    let resolveRef;
    let rejectRef;

    //create a new promise. Save the resolve and reject reference
    let dataPromise: Promise<void> = new Promise((resolve, reject) => {
        resolveRef = resolve;
        rejectRef = reject;
    });
    this.result = "";

    this._service.getOptionsQuestion(question_ID)
        .subscribe( (data: any) => {
            data.forEach(item => {
            console.log(item.Content);
            this.result += item.Content;
            });
            // resolve the promise once result is populated
            resolveRef(null);
        });

    //return promise created.
    return dataPromise;
}


// execute the console logs on then part of the promise returned by getAllOptions
this.getAllOptions(questionID).then(() => {
    console.log("++++++++++++++++++++++++++++++++");
    console.log(this.result);
});

Answer 4

To solve the problem, one approach is to utilize a promise in the getAllOptions function.

result: string;

getAllOptions(question_ID): Promise<void>{
    let resolveRef;
    let rejectRef;

    //create a new promise. Save the resolve and reject reference
    let dataPromise: Promise<void> = new Promise((resolve, reject) => {
        resolveRef = resolve;
        rejectRef = reject;
    });
    this.result = "";

    this._service.getOptionsQuestion(question_ID)
        .subscribe( (data: any) => {
            data.forEach(item => {
            console.log(item.Content);
            this.result += item.Content;
            });
            // resolve the promise once result is populated
            resolveRef(null);
        });

    //return promise created.
    return dataPromise;
}


// execute the console logs on then part of the promise returned by getAllOptions
this.getAllOptions(questionID).then(() => {
    console.log("++++++++++++++++++++++++++++++++");
    console.log(this.result);
});

Typescript: Delay code execution until a function has completed running

Answer №1

Answer №2

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