Deadfish
function run() {
var code = document.getElementById("code").value
var unicode = document.getElementById("unicode").checked
var n = 0
var output = ""
for (var i = 0; i < code.length; ++i) {
switch (code[i]) {
case "i":
n++
break
case "d":
n--
break
case "s":
n *= n
break
case "o":
if (unicode) {
output += String.fromCharCode(n)
} else {
output += n
output += "\n"
}
break
default:
output += "\n"
}
if (n == -1 || n == 256) {
n = 0
}
}
document.getElementById('output').value = output
}<div style="font-size:12px;font-family:Verdana, Geneva, sans-serif;">
<div style="float:left; width:50%;">
Code:<br>
<textarea id="code" rows="8" style="overflow:scroll;overflow-x:hidden;width:90%;" wrap="hard">iiisdsiiiiiiiioiiiiiiiiiiiiiiiiiiiiiiiiioiiiiiiiiiiiiiiiooiiiiiiiiiodddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddoddddddddddddddddddddddddsiioiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiioiiiiiiiiioiioddddddddddddoddddodddoiiiiiiiiiiiiiiiiiiiiiiiiodddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddodddddddddddddddddddddsdddddodddddodddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddodddddddddddddddddddddddsiiiiiiiioiiiiiiiiiiiiiiiiiiiiiioiiiiiiofdddddddddddddddddddddddddddddddddddddddddddddoiiiiiiiiiiiiiiiiiiiiiiiiioiiiiiiiiiiiiiiiooiiiiiiiiiodddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddoddddddddddddddddddddddddsiioiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiioiiiiiiiiioiioddddddddddddoddddodddoiiiiiiiiiiiiiiiiiiiiiiiiodddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddodddddddddddddddddddddsdddddodddddodddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddodddddddddddddddddddddddsiiiiiiiioiiiiiiiiiiiiiiiiiiiiiioiiiiiiofdddddddddddddddddddddddddddddddddddddddddddddoiiiiiiiiiiiiiiiiiiiiiiiiioiiiiiiiiiiiiiiiooiiiiiiiiiodddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddoddddddddddddddddddddddddsiioiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiioiiiiiiiiioiioddddddddddddoddddodddoiiiiiiiiiiiiiiiiiiiiiiiiodddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddoddddddddddddddddddddddddsiiiioiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiioddddoiiiiiiiiiiiiiiiiioddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddoddddddddddddddddddddddddsiiiioiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiioddddoiiioiioiiioiiiiiiiiiiodddddddddddofddddddddddddddddddddddddddddddddoiiiiiiiiiiiiiiiiiiiiiiiiioiiiiiiiiiiiiiiiooiiiiiiiiiodddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddoddddddddddddddddddddddddsiioiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiioiiiiiiiiioiioddddddddddddoddddodddoiiiiiiiiiiiiiiiiiiiiiiiiodddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddodddddddddddddddddddddsdddddodddddodddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddodddddddddddddddddddddddsiiiiiiiioiiiiiiiiiiiiiiiiiiiiiioiiiiiio</textarea>
<p>
<input id="unicode" type="checkbox" checked="true">Use ASCII/Unicode mode</input>
</p>
</div>
<div style="float:left; width:50%;">
Output:<br>
<textarea id="output" rows="6" style="overflow:scroll;width:90%;"></textarea>
<p>
<input id='run' type='button' value='Run' onclick='run()'></input>
</p>
</div>
</div>To pre-initialise the code box, just put something in between the textarea tags. Similarly, by adding checked="true" in the checkbox tag, you can have ASCII/Unicode mode on by default (as seen above).
Note that Deadfish itself doesn't actually have ASCII output in its original spec, I just put it in for questions which may allow "the next closest thing". If you're concerned that a question's rules may not allow Deadfish because of this, you can always look at something like Deadfish~ which does have ASCII output.
The example shown is from the Happy Birthday topic.