javascript – add text to a textarea without deleting the existing one

Question:

I have a textarea ( id='text'), where the user types his text freely (so far so good), at the end he clicks a button that inserts an example signature: "Typed by so and so".

When he inserts this new text the old one is removed, I would like to be able to add the new text without removing the old one. Does anyone have any tips/help?

Answer:

When you use el.value = 'foo'; you will delete the existing content and replace it with foo .
When you use el.value += 'foo'; you will keep the existing content and **add* foo .

Using += is a shortcut that in practice makes el.value = el.value + 'foo';

var textarea = document.querySelector('textarea');
var button = document.querySelector('button');
var assinatura = '\n\nCumprimentos,\nSuper heroi.'

button.addEventListener('click', function() {
  textarea.value += assinatura;
});

button {
    display: block;
}
textarea {
	height: 100px;
	width: 200px;
}

<textarea name="texto" id="texto"></textarea>
<button type="button">Assinar</button>

jsFiddle: https://jsfiddle.net/tbn7y4L7/