tests passing. functions descriptions/tests could be more clear.

solution.js

@@ -1,5 +1,135 @@
 const { nums, words } = require("./data/data.js");
 
+
+class Node {
+  constructor(data){
+    this.data = data
+    this.next = null
+  }
+}
+
+class LinkedList{
+  constructor(head = null){
+    this.head = head
+  }
+  // - `insert`
+  insert(val){
+    const newNode = new Node(val)
+    const curr = this.head
+    this.head = newNode
+    newNode.next = curr
+  }
+  // - `size`
+  size(){
+    let curr = this.head
+    let count = 0
+    while(curr){
+      count++
+      curr = curr.next
+    }
+    return count
+  }
+  // - `delete` by key 
+
+  //not sure if key is value of data or the index in the list. Wish it was more discriptive/clear  
+  delete(key){
+    if(!key){
+      this.head = this.head.next
+    }else{
+      let c = 1
+      let prev = this.head
+      let curr = this.head.next
+      let next
+      while(c <= key){
+        if(c === key){
+          prev.next = curr.next
+        }
+        c++
+        next = curr.next
+        prev = curr
+        curr = next
+    }
+    }
+  }
+  // - `getFirst` element
+  getFirst(){
+    return this.head
+  }
+  // - `getLast` element
+  getLast(){
+    let curr = this.head
+    while(curr.next){
+      curr = curr.next
+    }
+    return curr
+  }
+  // - `search` an element by key and return data    const nums = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 0];
+  search(key){
+    let curr = this.head
+    while(curr){
+      if(curr.data === key){
+        return curr
+      }
+      curr=curr.next 
+    }
+  }
+  // - `getKth` retrieve kth element  
+  getKth(key){
+    let curr = this.head
+    let c = 1
+    while(curr){
+      if(c === key){
+        return curr
+      }
+      curr=curr.next 
+      c++
+    }
+  }
+  // - `getKthToLast` retrieve kth from last element
+  getKthToLast(k){
+    let index = this.size() - k
+    let curr = this.head
+    while(curr){
+      if(index==1){
+        return curr
+      }
+      curr = curr.next
+      index--
+    }
+  }
+  // - `isEmpty` check if list is empty
+  isEmpty(){
+    return this.head === null
+  }
+  // - `clear` the linked list
+  clear(){
+    this.head = null
+  }
+  // - `toArray`convert data from linked list to an array
+  toArray(){
+    let curr = this.head
+    const arr = []
+    while(curr){
+      arr.push(curr.data)
+      curr = curr.next
+    }
+    return arr
+  }
+  // - `containsDuplicates` check for duplicates - return true if contains duplicates, false if not
+  containsDuplicates(){
+    let curr = this.head
+    let set = new Set()
+    while(curr){  
+      if(!set.has(curr.data)){
+        set.add(curr.data)
+        curr = curr.next
+      }else{
+        return true
+      }
+    }
+    return false
+  }
+}
 module.exports = {
   Node,
   LinkedList,