Is there a way to change a typescript callback into a promise?

Question

Is there a way to change a typescript callback into a promise?

I am looking to create a method within my class that connects to a MySQL database. I have already written my SQL code and now I want to move away from using callbacks and start implementing promises, as it is more modern.

Below is my function with callbacks (old school):

public does_player_exist(username: string, callback: any) {
    this.mysql.connect();
    this.mysql.query('USE devdb');
    this.mysql.query('SELECT p_name FROM players WHERE p_name = "'+username+'"', (err: Error, result: any[]) {
        if (result.length === 1) {
            callback(true)
        } else {
            callback(false);
        }
    });
}

Next is the method where I attempted to use a promise, but unfortunately failed:

public does_player_exist(username: string): Promise<boolean> {
    this.mysql.connect();
    this.mysql.query('USE devdb');
    return this.mysql.query('SELECT p_name FROM players WHERE p_name = "'+username+'").toPromise().then((result) => {
        return result.length === 1;
    })
}

When I invoke this method:

service.does_player_exist('test').then((result) => { console.log(result) })

I am hopeful that someone can assist me with this transition, as I am eager to embrace more modern practices and move away from the old school ways xD

Thank you in advance.

mysql typescript promise

Answer 1

Answer №1

Start by creating a new Promise and resolve/reject it within the callback functions of the query method. Then, return this promise. As a result, the does_player_exist method will now return a Promise object, allowing you to access functions like "then".

public does_player_exist(username: string, callback: any): Promise<boolean> {
    this.mysql.connect();
    this.mysql.query('USE devdb');
    var promise = new Promise<boolean>();
    this.mysql.query('SELECT p_name FROM players WHERE p_name = "'+username+'"', (err: Error, result: any[]) {
        if (!err) promise.resolve(!!result.length);            
        else promise.reject();
    });
    return promise;
}

It is important to ensure that the Promise class is available in your environment for this code to run successfully.

Additionally, remember to sanitize your input (username) to prevent vulnerabilities in your application and protect against potential attackers.

Answer 2

Start by creating a new Promise and resolve/reject it within the callback functions of the query method. Then, return this promise. As a result, the does_player_exist method will now return a Promise object, allowing you to access functions like "then".

public does_player_exist(username: string, callback: any): Promise<boolean> {
    this.mysql.connect();
    this.mysql.query('USE devdb');
    var promise = new Promise<boolean>();
    this.mysql.query('SELECT p_name FROM players WHERE p_name = "'+username+'"', (err: Error, result: any[]) {
        if (!err) promise.resolve(!!result.length);            
        else promise.reject();
    });
    return promise;
}

It is important to ensure that the Promise class is available in your environment for this code to run successfully.

Additionally, remember to sanitize your input (username) to prevent vulnerabilities in your application and protect against potential attackers.

Answer 3

Answer №2

Here are some tips for improving your database connection:

1. Consider using a factory function to create and reuse connections.

2. Utilize prepared statements to avoid SQL injection vulnerabilities. You can learn more about this here.

3. Try using a promise library like Bluebird or Q for easier asynchronous operations. These libraries offer handy utility methods such as promisify, which can convert callback functions into promise-returning functions.

// This snippet demonstrates how you can implement the above tips
public query() {
    this.mysql.connect();
    this.mysql.query('USE devdb');

    return Promise.promisify(this.mysql.query.bind(this.mysql))
}

public does_player_exist(username: string): Promise<boolean> {
    return this
        .query('SELECT p_name FROM players WHERE p_name = ?', [username])
        .then(result => result.length === 1);
}

Answer 4

Here are some tips for improving your database connection:

1. Consider using a factory function to create and reuse connections.

2. Utilize prepared statements to avoid SQL injection vulnerabilities. You can learn more about this here.

3. Try using a promise library like Bluebird or Q for easier asynchronous operations. These libraries offer handy utility methods such as promisify, which can convert callback functions into promise-returning functions.

// This snippet demonstrates how you can implement the above tips
public query() {
    this.mysql.connect();
    this.mysql.query('USE devdb');

    return Promise.promisify(this.mysql.query.bind(this.mysql))
}

public does_player_exist(username: string): Promise<boolean> {
    return this
        .query('SELECT p_name FROM players WHERE p_name = ?', [username])
        .then(result => result.length === 1);
}

Answer 5

Answer №3

I developed a straightforward npm package to accomplish this while maintaining type safety:

ts-promisify-callback

This solution necessitates the usage of typescript@^4.0 (upcoming release) and is currently limited to handling callbacks in the common format of (err, result) => {}.

Answer 6

I developed a straightforward npm package to accomplish this while maintaining type safety:

ts-promisify-callback

This solution necessitates the usage of typescript@^4.0 (upcoming release) and is currently limited to handling callbacks in the common format of (err, result) => {}.

Is there a way to change a typescript callback into a promise?

Answer №1

Answer №2

Answer №3

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