setInterval
HTML
<div id="terminal-screen-1">
</div>
CSS
#terminal-screen-1, #terminal-screen-2, #terminal-screen-3 {
width: 100%;
padding: 30px
}
#terminal-screen-1 {
background: cyan;
color: black
}
JavaScript
var string = "Hello!";
var index = 0;
var characterSequence = setInterval(function() {
$('#terminal-screen-1').append(string[index]);
index++
if (index >= string.length) clearInterval(characterSequence);
}, 50);