for..in order

Prior to ES2020, the specifications did not specify in which order for (a in b) should run. Even though most of the javascript engines/browsers loop over the properties of an object in the order in which they were defined, it is not the case with all scenarios. This has been officially standardized in ES2020.

var object = {
'a': 2,
'b': 3,
'c': 4
}

for(let key in object) {
console.log(key); // a b c
}

ES2021 Or ES12

ECMAScript 2021 or ES12 has been released in mid of 2021 with few important features which can be used JavaScript.