Public property in class member definition

The proposal is an enhancement of public property of class definition syntax.

The proposal will implementation public keyword in class definition:

• Nothing NEW

  Concept cleanly. All the features are grammatical sugar, except that the public keyword is enabled.

The proposal is not tc39 officailly now but implemented at prepack-core with proposal-public-property (@here).

You could see more test case in this project (@here).

Table of Contents

• Public property in class member definition
  • Syntax design
  • Concepts
  • Implementation
  • Testcases
  • References
  • History

Syntax design

Key principle:

​ All the features of grammatical sugar can be implement base on existing.

1. using public define public property, or default

Ex:

class f {
  public data = 100;
  public static data = 200;
}

// equal
let f = class {};
let defaultAttr = { writable: true, enumerable: true, configurable: true };
Object.defineProperty(f.prototype, 'data', {value: 100, ...defaultAttr});
Object.defineProperty(f, 'data', {value: 200, ...defaultAttr});

case 2:

class f {
  public foo() {
    // enabled, can be remove `public`
  }

  // equal
  foo() {
  }
}

2. publish member from private scope

example, for private property:

class MyClass {
  private x = 100;
  public as x;
}

// equal
class MyClass {
  private x = 100;

  get x() {
    return x;
  }
  set x(v) {
    x = v;
  }
}

case 2, for protected property:

class MyClass {
  protected x = 100;
}

class MyClassEx extends MyClass {
  public as x; // accept
}

3. publish with alias

Ex:

class MyClass {
  protected x = 100;
}

class MyClassEx extends MyClass {
  public x as valueX;  // alias `valueX`
}

// equal
class MyClassEx extends MyClass {
  get valueX() {
    return x;
  }
  set valueX(v) {
    x = v;
  }
}

Concepts

The truth is "All the normal properties are published in JavaScript".

Implementation

Core rules:

• Can not publish a no-private member using public as syntax.
• Can not assignment initialization value when public as a member.

Key implementation steps:

• eta public keyword when evaluate definition item.
• make get and set method for "public [name] as <name>" grammatical.

Done.

Testcases

The proposal has full test case in repository, current syntax based.

# install test framework
> mkdir node_modules
> npm install fancy-test chai mocha --no-save
# test it
> mocha

# (OR)
> bash run.sh

References

• Objections to fields, especially the private field syntax
• The proposal should be rejected!
• My comments at #100

History

2019.09.11 initial release.