Linked List Operations on javascript

LinkedList.js

function Node(value){
  this.value = value;
  this.next = null;
}
function LinkedList() {
  this.start = null;
  this.length = 0;
}

LinkedList.prototype.push = function (val) {

  if(this.start === null) {
    this.start = new Node(val);
  }
  else {
    var currentNode = this.start;
    while (currentNode != null) {
      if (currentNode.next == null) {
        currentNode.next = new Node(val);
        this.length++;
        return true;
      }
      currentNode = currentNode.next;
    }

  }
}

LinkedList.prototype.searchByIndex = function (index) {
  if (index >= this.length) {
    return null;
  }
  if (index === 0) {
    return this.start;
  } else {
    var currentNode = this.start.next;
    for (var i = 1; i <= index; i++) {
      if (i === index) {
        return currentNode;
      }
      currentNode = currentNode.next;
    }
  }
}

LinkedList.prototype.search = function (val) {
  if (this.start === null) {
    return null;
  }
  else {
    var currentNode = this.start;
    while (currentNode != null) {
      if (currentNode.value == val) {
        return currentNode;
      }
      currentNode = currentNode.next;
    }
  }
}

LinkedList.prototype.remove = function (val) {
  if(this.start === null) {
    return false;
  }
  if(this.start.value === val) {
    if (this.start.next) {
      this.start = this.start.next;
    } else {
      this.start = null;
    }
    this.length--;
    return true;
  }
  else {
    var previousNode = this.start;
    var currentNode = this.start.next;
    while (currentNode != null) {
      if (currentNode.value == val) {
        previousNode.next = currentNode.next;
        this.length--;
        return true;
      }
      previousNode = currentNode;
      currentNode = currentNode.next;
    }

  }
}

/*
  Test your code through here(main func)
*/
function testCode() {
  var test = [9,5,7,6,8,4,11,20,3,17,19,1,45,2];

  var linkedList = new LinkedList();
  var start = new Node(test[0]);
  linkedList.start = start;

  for(var i = 1; i < test.length; i++) {
    linkedList.push(test[i]);
  }
  console.log('Linked List:',JSON.stringify(linkedList));
  linkedList.remove(9);
  console.log('Removed 9 from Linked List:',JSON.stringify(linkedList));
  linkedList.remove(11);
  console.log('Removed 11 from Linked List:',JSON.stringify(linkedList));

  console.log('search 17:', linkedList.search(17));
  console.log('search Non Existing:', linkedList.search('abc'));

  console.log('searchByIndex index 6(value 3):', linkedList.searchByIndex(6));
  console.log('searchByIndex Non Existent(length higher):', linkedList.searchByIndex(7776));
  console.log('searchByIndex Non Existent(string):', linkedList.searchByIndex('abc'));
}
//running the main func to test the code...
testCode();