Is It Statistically Safe To Use Proposals In Stage 3 Of Ecma?

Background I am referring to the ... operator. Many people like and support the idea of doing the following: const obj = { 'hello': 1 }; const obj2 = { 'world': 2, ...obj }; Probl

Solution 1:

What are probabilities of backwards compatibility changes in S3?

Low without returning to Stage 2 (see next question).

How many proposals have been withdrawn at S3 ?

It's rare, but it does happen. For instance, decorators was Stage 3 for some time but has been rolled back to Stage 2. Similarly, class fields were at Stage 3 but moved back to Stage 2 in November (and have since been split [again], where the Class Public Instance Fields & Private Instance Fields proposal went back to Stage 3 again, leaving Static class fields and private static methods at Stage 2).

You can get an idea of how things move by reviewing the history on the README.md for https://github.com/tc39/proposals. It can be a bit of a pain, though.

Is it statistically safe to use proposals in Stage 3 of ECMA?

It depends on what you mean by "statistically safe." If you want a high degree of certainty, restrict yourself to Stage 4.

Specifically in regard to object rest/spread, it's implemented (not behind a flag) in current versions of V8 shipping in Chrome and SpiderMonkey shipping in Firefox. Try it here:

const a = {answer: 42};
const b = {question: "Life, the Universe, and Everything", ...a};
console.log(b);

On the first day of the TC39 meeting in November, the status update was:

KCL: Is Object spread possible to make it into es2018?

BT: If someone can make a PR and get it on the January agenda then we can put it in.

...which sounds like Stage 4 in January is likely.