<p>Write a function to implement a Brain**** interpreter. The function will take a string as a parameter and should return a string as the output. More details are given below : </p>
<p>RCBF is a set of <ahref="http://rosettacode.org/wiki/Brainf***"title="Brainf***">Brainf***</a> compilers and interpreters written for Rosetta Code in a variety of languages.</p><p>Below are links to each of the versions of RCBF.</p><p>An implementation need only properly implement the following instructions:</p>
<p>{|</p>
<p>!Command</p>
<p>!Description</p>
<p>|-</p>
<p>| style="text-align:center"| <code>></code> || Move the pointer to the right</p>
<p>|-</p>
<p>| style="text-align:center"| <code><</code> || Move the pointer to the left</p>
<p>|-</p>
<p>| style="text-align:center"| <code>+</code> || Increment the memory cell under the pointer</p>
<p>|-</p>
<p>| style="text-align:center"| <code>-</code> || Decrement the memory cell under the pointer</p>
<p>|-</p>
<p>| style="text-align:center"| <code>.</code> || Output the character signified by the cell at the pointer</p>
<p>|-</p>
<p>| style="text-align:center"| <code>,</code> || Input a character and store it in the cell at the pointer</p>
<p>|-</p>
<p>| style="text-align:center"| <code>[</code> || Jump past the matching <code>]</code> if the cell under the pointer is 0</p>
<p>|-</p>
<p>| style="text-align:center"| <code>]</code> || Jump back to the matching <code>[</code> if the cell under the pointer is nonzero</p>
<p>|}</p>
<p>Any cell size is allowed, EOF (<u>E</u>nd-<u>O</u>-<u>F</u>ile) support is optional, as is whether you have bounded or unbounded memory.</p>
let hello='++++++++[>++++[>++>+++>+++>+<<<<-]>+>+>->>+[<]<-]>>.>---.+++++++..+++.>>.<-.<.+++.------.--------.>>+.>++.'
let bye='++++++++++[>+>+++>++++>+++++++>++++++++>+++++++++>++++++++++>+++++++++++>++++++++++++<<<<<<<<<-]>>>>+.>>>>+..<.<++++++++.>>>+.<<+.<<<<++++.<++.>>>+++++++.>>>.+++.<+++++++.--------.<<<<<+.<+++.---.';
```
</div>
</section>
## Solution
<sectionid='solution'>
```js
function brain(prog){
var output="";
var code; // formatted code
var ip = 0; // current instruction within code
var nest = 0; // current bracket nesting (for Out button)
var ahead = []; // locations of matching brackets
var data = [0]; // data array (mod by +, -)
var dp = 0; // index into data (mod by <, >)
var inp = 0; // current input character (fetch with ,)
var quit = 0;
var commands = {
'>':function() { if (++dp >= data.length) data[dp]=0 },
'<':function() { if (--dp <0)quit++},
'+':function() { ++data[dp] },
'-':function() { --data[dp] },
'[':function() { if (!data[dp]) ip = ahead[ip]; else ++nest },
']':function() { if ( data[dp]) ip = ahead[ip]; else --nest },
',':function() {
var c = document.getElementById("input").value.charCodeAt(inp++);
data[dp] = isNaN(c) ? 0 : c; // EOF: other options are -1 or no change
},
'.':function() {
output+=String.fromCharCode(data[dp]);
/*var s = document.getElementById("output").innerHTML)
+ String.fromCharCode(data[dp]);
s = s.replace(/\n/g,"<br>").replace(/ /g,"&nbsp;");