let btn = document.getElementById("btn");
let output = document.getElementById("output");
let quotes = [
  "The greatest glory in living lies not in never falling, but in rising every time we   fall. -Nelson Mandela",
  "The way to get started is to quit talking and begin doing. -Walt Disney",
  "Your time is limited, so don't waste it living someone else's life. Don't be trapped by dogma – which is living with the results of other people's thinking. -Steve Jobs",
  "If life were predictable it would cease to be life, and be without flavor. -Eleanor Roosevelt",
  "If you look at what you have in life, you'll always have more. If you look at what you don't have in life, you'll never have enough. -Oprah Winfrey",
  "If you set your goals ridiculously high and it's a failure, you will fail above everyone else's success. -James Cameron",
  "Life is what happens when you're busy making other plans. -John Lennon",
];
btn.addEventListener("click", function() {
  let randomQuote = quotes[Math.floor(Math.random() * quotes.lenth)];
  output.innerHTML = randomQuote;
});

<h1>Quote Generator</h1>
<div class="content">
  <button id="btn">Press for a new Quote!</button>
  <p id="output">Press the button to generate a quote.</p>
</div>