The major JS frameworks have all been around for 5 years; several for 10 (react turns 10 this May).
Compare that to the average tech employee tenure, or even the average lifetime of a startup company.
Compare that to the average tech employee tenure, or even the average lifetime of a startup company.
Now that's commitment to backward compatibility (and they can't have it any other way, they won't rewrite half of facebook just because their own framework changed).