Class members in TypeScript

Access modifiers, parameter properties, and the two kinds of private.

class Session {
  #secret = "hidden";
  protected runs: number[] = [];

  constructor(
    public readonly lang: string,
    private target = 90,
  ) {}

  record(tpm: number): this {
    this.runs.push(tpm);
    return this;
  }

  get stars(): number {
    return Math.max(...this.runs) >= this.target ? 3 : 1;
  }

  reveal(): string {
    return this.#secret;
  }
}

class Timed extends Session {
  get count(): number {
    return this.runs.length; // protected: visible here
  }
}

const timed = new Timed("ts", 95).record(98) as Timed;
console.log(timed.lang, timed.stars, timed.count, timed.reveal());

How it works

1. private is compile-time; #field is enforced at run time.
2. A parameter property declares and assigns in one place.
3. protected is visible to subclasses, readonly to no writer.

Keywords and builtins used here

• Math
• as
• class
• const
• constructor
• extends
• number
• private
• protected
• public
• readonly
• return
• string
• this

The run, in numbers

Lines

31

Characters to type

557

Tokens

158

Three-star pace

100 tpm

At the three-star pace of 100 tokens a minute, this run takes about 95 seconds.

Type this snippet

Step 2 of 4 in Classes, step 2 of 19 in Classes & patterns.

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