The challenge with the preceding approach is that the collections that we're concatenating together could actually be indexed sequences, capable of evaluating lazily. If you concatenate them into a list, then you lose any benefit to lazy evaluation. Instead, you can call the concat() method on a sequence:

const mySeq1 = Range(1, 6)
  .filterNot((v) => {
    console.log('mySeq1', v);
    return v % 2;
  });
const mySeq2 = Range(6, 11)
  .filterNot((v) => {
    console.log('mySeq2', v);
    return v % 2;
  });

Seq()
  .concat(mySeq1, mySeq2)
    .forEach(v => console.log('result', v));
    // -> mySeq1 1
    // -> mySeq1 2
    // -> result 2
    // -> mySeq1 3
    // -> mySeq1 4
    // -> result 4
    // -> mySeq1 5
    // -> mySeq2 6
    // -> result 6
    // -> mySeq2 7
    // -> mySeq2 8
    // -> result 8
    // -> mySeq2 9
    // -> mySeq2 10
    // -> result 10

Using this approach, you can lazily concatenate sequence values together as the forEach() side-effect iterates over the result. You can see how lazy evaluation works in the preceding example from the logging added in the filterNot() predicates.