To Do List JS

var buttons = document.querySelectorAll("button");
var button = buttons[0];
var input = document.getElementById("user_input");
var ul = document.querySelector("ul");
var lis = document.querySelectorAll("li");
var listItems = [];

lis.forEach(function (li) {
  listItems.push(li.textContent);
});

function isNotBlank() {
  return input.value.length > 0;
}

function keyPressEnter() {
  return event.keyCode === 13;
}

function elementType() {
  return event.path[0].tagName.toLowerCase();
}

function isButtonEvent() {
  return elementType() === "button";
}

function isInputEvent() {
  return elementType() === "input";
}

function isNewListItem() {
  var included = listItems.includes(input.value);
  if (included) {
    alert(input.value + " is already on the list!");
    input.focus();
    return false;
  } else {
    return true;
  }
  return !listItems.includes(input.value);
}

function isValidlyEntered() {
  return isNotBlank() && isNewListItem();
}

function isValidButtonInput() {
  return isButtonEvent() && isValidlyEntered();
}

function isValidKeyboardInput() {
  return isInputEvent() && keyPressEnter() && isValidlyEntered();
}

function isValidInput() {
  return isValidButtonInput() || isValidKeyboardInput();
}

function createListElement() {
  var li = document.createElement("li");
  li.appendChild(document.createTextNode(input.value));
  ul.appendChild(li);
  input.value = "";
}

function addToList() {
  if (isValidInput()) {
    createListElement();
    input.focus();
  }
}

button.addEventListener("click", addToList);
input.addEventListener("keypress", addToList);
input.focus();