Unable to convert class-based Linked List to function-based Linked List

Okay so I’m learning Data Structures where my tutorial is following class-based approach. So now I am trying to convert it to functions as I want to practice Linked Lists on Leetcode and Leetcode follows the functional approach. Can anybody help me with the conversion? I need only one method to be converted and I’ll be able to do the rest of them.

Here’s the class-based approach:

class Node {
    constructor( val ) {
        this.val = val;
        this.next = null;
    }
}

class SinglyLinkedList {
    constructor () {
        this.head = null;
        this.tail = null;
        this.length = 0;
    }

    push( val ) {
        const newNode = new Node( val );

        if ( !this.head ) {
            this.head = newNode;
            this.tail = this.head;
        } else {
            this.tail.next = newNode;
            this.tail = newNode;
        }
        this.length++
        return this;
    }

}

const list = new SinglyLinkedList();

list.push( 'HELLO' );
list.push( 'WORLD' );

Here’s what I tried so far to achieve function-based approach:

function Node( val ) {
  this.val = val;
  this.next = null;
}

let head = null;
let tail = null;
let length = 0;

const SinglyLinkedListFunc = function() {
    const newNode = new Node( 'HELLO' );
};

SinglyLinkedListFunc()

This is what I could achieve so far. And I’m stuck with it and I don’t know what to do next. Someone please help