Sequence creation and iteration

There are two ways to create sequences: you can directly create sequence instances, passing them collection data, or you can transform existing collections, such as lists and maps, into sequences.

Basic sequence creation

You can create new sequences by passing the Seq() constructor JavaScript arrays or objects, as follows:

import { Seq } from 'immutable';

const myIndexedSeq = Seq([1, 2, 3]);
const myKeyedSeq = Seq({ one: 1, two: 2, three: 3 });

console.log('myIndexedSeq', myIndexedSeq.toJS());
// -> myIndexedSeq [ 1, 2, 3 ]
console.log('myKeyedSeq', myKeyedSeq.toJS());
// -> myKeyedSeq { one: 1, two: 2, three: 3 }

There are actually two types of sequence collections: Seq.Indexed and Seq.Keyed. The Seq() constructor, which is really just a function due to the absence of the new keyword, will return the correct type of collection depending on what's passed to it.

Note

Generally speaking, you don't have to worry about the distinction between indexed and keyed...