namespace SLL {        
    class Node {
        constructor(
            public data, 
            public next: Node = null,
        ) {}
    }    
    // export class so it can be used outside namespace
    export class List {  
        private head;
        push(data) {
            const node = new Node(data);
            node.next = this.head;
            this.head = node;
        }
    }
}

const list = new SLL.List();
for (let i=3; i>0; i--) { list.push(i); }
console.log(list);