Interposing means inserting the same value in-between every value in the indexed collection. Interleaving is like concatenation, except that the order of the resulting values is alternated between input lists based on the order of the collection arguments.
Sometimes you need to separate your collection values using a static value. You could, for example, add this value to your side-effect as needed. The downside to this approach is that you would then have a side-effect code that now has to do something that's better handled by the Immutable.js chaining pattern.
Using the interpose() method, you can maintain the chainable method call pattern while passing separator data to your side-effects. Moreover, you can do this lazily as follows:
const myList = List.of(1, 2, 3, 4, 5, 6, 7, 8);
myList
.toSeq()
.filter((v) => {
console.log('filtering', v);
return v % 2;
})
.interpose('...')
.forEach(v => console.log(v));
/...