Just assign an id to your textarea, and use document.getElementById:
<textarea name="text" placeholder="Type your text here!" id="myTextarea"></textarea>
<a href="" onclick="myFunction(document.getElementById('myTextarea').value); return false;">Send!</a>
Alternatively, you could instead change your myFunction function, to make it define the value inside the function:
JS:
function myFunction() {
var value = document.getElementById('myTextarea').value;
//rest of the code
}
HTML:
<textarea name="text" placeholder="Type your text here!" id="myTextarea"></textarea>
<a href="" onclick="myFunction(); return false;">Send!</a>
And if you're using jQuery, which it does look like you do, you could change the document.getElementById('myTextarea').value to $('#myTextarea').val(); to get the following:
JS:
function myFunction() {
var value = $('#myTextarea').val();
//rest of the code
}
HTML:
<textarea name="text" placeholder="Type your text here!" id="myTextarea"></textarea>
<a href="" onclick="myFunction(); return false;">Send!</a>