Static this

[felixfbecker]

Consider this implmentation of a ORM-like Model class:

class Model {
    public static tableName: string;
    public static findById(id: number): this { // error: a this type is only available in a non-static member of a class or interface 
        const rows = db.query(`SELECT * FROM ${this.tableName} WHERE id = ?`, [id]);
        const instance = new this();
        for (const column of rows[0]) {
            instance[column] = rows[0][column];
        }
        return instance;        
    }
}

class User extends Model {
    public static tableName = 'users';
    public username: string;    
}

const user = User.findById(1); // user instanceof User

Currently, this is not possible, because TypeScript does not allow this in static members. There is no reason for this limitation: this inside a static method is simply the class in JavaScript (aka typeof Model or typeof User, depending on what class this is called on).

[yortus]

Duplicate/related: #5863