How to access static members from instance methods in typescript?

Question

I try to use a static member from an instance method. I know about accessing static member from non-static function in typescript, but I do not want to hard code the class to allow inheritance:

class Logger {
  protected static PREFIX = '[info]';

  public log(msg: string) {
    console.log(Logger.PREFIX + ' ' + msg); // What to use instead of Logger` to get the expected result?
  }
}

class Warner extends Logger {
  protected static PREFIX = '[warn]';
}

(new Logger).log('=> should be prefixed [info]');
(new Warner).log('=> should be prefixed [warn]');

I've tried things like

typeof this.PREFIX

TLDR - `ClassName.property`. For overridden properties, `( this.constructor).property`. — nathanfranke, Oct 02 '20 at 18:56

basarat · Accepted Answer · 2023-02-20T20:51:49.657

46

You simply need ClassName.property :

class Logger {
  protected static PREFIX = '[info]';
  public log(message: string): void {
    alert(Logger.PREFIX + string); 
  }
}

class Warner extends Logger {
  protected static PREFIX = '[warn]';
}

MORE

from : https://basarat.gitbook.io/typescript/future-javascript/classes

TypeScript classes support static properties that are shared by all instances of the class. A natural place to put (and access) them is on the class itself and that is what TypeScript does:

class Something {
    static instances = 0;
    constructor() {
        Something.instances++;
    }
}

var s1 = new Something();
var s2 = new Something();
console.log(Someting.instances); // 2

UPDATE

If you want it to inherit from the particular instance's constructor use this.constructor. Sadly you need to use some type assertion. I am using typeof Logger shown below:

class Logger {
  protected static PREFIX = '[info]';
  public log(message: string): void {
    var logger = <typeof Logger>this.constructor; 
    alert(logger.PREFIX + message); 
  }
}

class Warner extends Logger {
  protected static PREFIX = '[warn]';
}

edited Feb 20 '23 at 20:51

answered Mar 24 '15 at 22:42

basarat

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8

I know about using the ClassName.property. But then it will use Logger.PREFIX even in subclasses that have their own .PREFIX defined. – Simon Hürlimann Mar 25 '15 at 08:17
Updated the question to be more clear about the expected result. – Simon Hürlimann Mar 25 '15 at 08:31
@SimonHürlimann Updated the answer to take that into account ;) – basarat Mar 25 '15 at 08:31
It seems I can use `` instead of `` in the typecast. This seems more appropriate. – Simon Hürlimann Mar 25 '15 at 08:35
@SimonHürlimann I knew I was being lazy and hence left ambiguity with *some*. Thanks for clearing that up. Example updated for future peeps :) – basarat Mar 25 '15 at 08:39
Any way to make this work if Logger.log is static? I would really need that behavior, but can't seem to find out how to do it. – Ludwik Aug 15 '16 at 13:24
4

This does not work. For example: ``` const a = new Logger(); a.log('a ') const b = new Warner(); b.log('b ') ``` Both log Info – Jimmy Kane Sep 17 '17 at 12:41
1

Why this answer is voted up? Warner instance printed out [info] – Long Nguyen Jul 11 '22 at 14:20
@JimmyKane: Your example works correctly for me (after changing `alert()` to `console.log()`) with node v16.17.0, TS v4.4.2. – j_random_hacker Feb 15 '23 at 00:39

How to access static members from instance methods in typescript?

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