//index.html

<div id="password-container">
    <div id="password-header">
      <h3>Please login to retrieve trip details or save a new trip</h3>
    </div>
    <form id="login" method="post" name="login">
      <label>Username :</label>
      <input type="text" name="username" id="username"/>
      <label>Password :</label>
      <input type="password" name="password" id="password"/>
      <input type="button" value="Login" id="submit" onclick="validate()"/>
    </form>
  </div>

//login.js

var testLogin = [
{
  username: "Adrian",
  password: "password"
},
{
 username: "Max",
 password: "12345"
},
{
  username: "Ross",
  password: "testing"
},
{
  username: "Tom",
  password: "TheFace"
}
]

validate = function() {
  var username = document.getElementById("username").value
  var password = document.getElementById("password").value

  for (var i = 0; i < testLogin.length; i++) {
    if (username == testLogin[i].username && password == testLogin[i].password) {
      alert(username + " is logged in!")
      //window.location = where do we want to go?
      return;
    }
  }
  alert("incorrect username or password")
}