Status of TypeScript's 3.7 iteration plan for language standard conformance with ECMAScript's private fields proposal.

1. TypeScript 3.7 Language
Standard Conformance
ECMAScript Private Fields

2. Private Fields
• Prevent users from relying on internals which may change
• Specified by TC39 (Technical Committee 39)
• Authors: Daniel Ehrenberg (Igalia), Jeff Morrison (Facebook)
• Merged with class field declarations proposal
• Stage 3 (Strawperson, Draft, Candidate, Finished)
• Awaits feedback: https://github.com/tc39/proposal-class-fields
• Available online: https://tc39.es/proposal-class-fields/
2019/12/17

3. ECMAScript Syntax
class Point {
#x;
#y;
constructor(x, y) {
this.#x = x;
this.#y = y;
}
equals(point) {
return this.#x === point.#x && this.#y === point.#y;
}
}
const p1 = new Point(1, 2);
const p2 = new Point(1, 2);
p1.equals(p2); // true
2019/12/17

4. TypeScript Counterpart
class Point {
private x: number;
private y: number;
constructor(x: number, y: number) {
this.x = x;
this.y = y;
}
equals(point: Point) {
return this.x === point.x && this.y === point.y;
}
}
const p1 = new Point(1, 2);
const p2 = new Point(1, 2);
p1.equals(p2); // true
2019/12/17

5. Implementation Status
• Introduced in Chrome 74
• “SyntaxError: private fields are not currently supported” in Firefox 71
• Expected with TypeScript 3.7
https://github.com/microsoft/TypeScript/issues/33352
2019/12/17

6. Implementation Status
https://github.com/microsoft/TypeScript/issues/33925#issuecomment-542925717
2019/12/17