Mastering Immutable.js

No defined iteration order

Sets are like maps in that they don't have a defined iteration order. This means that using a for...of loop or the forEach() method could have unexpected results, as follows:

console.log('myList.forEach()');myList.forEach(v => console.log(v));// -> myList.forEach()// -> 1// -> 2// -> 3console.log('mySet.forEach()');mySet.forEach(v => console.log(v));// -> mySet.forEach()// -> 1// -> 2// -> 3

When a collection isn't indexed numerically, don't count on consistent iteration behavior. You could end up seeing consistent iteration behavior in one JavaScript engine and a different behavior in another. The iteration behavior of sets is stable, meaning that the order doesn't change once it's already been iterated over, but ...