Brainfuck interpreter

brainfuck.js

// Here's a relatively verbose version that is somewhat easier to read
////////////////////////////////////////

let program = '+++>++<[->+<]>.';
let arr = [];
let dataPointer = 0;
let instructionPointer = 0;
let output = '';

while (program[instructionPointer]) {
	switch (program[instructionPointer]) {
		// Increment the data pointer (to point to the next cell to the right).
		case '>':
			dataPointer++;
		break;
		// Decrement the data pointer (to point to the next cell to the left).
		case '<':
			dataPointer--;
		break;
		// Increment (increase by one) the byte at the data pointer.
		case '+':
			arr[dataPointer] = (arr[dataPointer] || 0) + 1;
		break;
		// Decrement (decrease by one) the byte at the data pointer.
		case '-':
			arr[dataPointer] = (arr[dataPointer] || 0) - 1;
		break;
		// Output the byte at the data pointer.
		case '.':
			output += arr[dataPointer]
		break;
		// Accept one byte of input, storing its value in the byte at the data 
		// pointer.
		case ',':
			arr[dataPointer] = parseInt(prompt());
		break;
		// If the byte at the data pointer is zero, then instead of moving the
		// instruction pointer forward to the next command, jump it forward to
		// the command after the matching ] command.
		case '[':
			if (! arr[dataPointer])
				while (program[instructionPointer] != ']')
					instructionPointer++;
		break;
		// If the byte at the data pointer is nonzero, then instead of moving the
		// instruction pointer forward to the next command, jump it back to the
		// command after the matching [ command.
		case ']':
			if (arr[dataPointer])
				while (program[instructionPointer] != '[')
					instructionPointer--;
		break;
	}
	instructionPointer++;
}
console.log(output);




// Here's a version that starts to bring the character count down
////////////////////////////////////////

let program = '[->+<]>.';
let arr = [2,2];
let dataPointer = 0;
let instructionPointer = 0;
let output = '';

const instructions = '><+-.,[]';
const funcs = [
	() => dataPointer++,
	() => dataPointer--,
	() => arr[dataPointer] = (arr[dataPointer] || 0) + 1,
	() => arr[dataPointer] = (arr[dataPointer] || 0) - 1,
	() => output += arr[dataPointer],
	() => arr[dataPointer] = parseInt(prompt()),
	() => {if (! arr[dataPointer]) while (program[instructionPointer] != ']') instructionPointer++},
	() => {if (arr[dataPointer]) while (program[instructionPointer] != '[') instructionPointer--},
]

while (i = program[instructionPointer]) {
	funcs[instructions.indexOf(i)]();
	instructionPointer++;
}
console.log(output);




// This version is just 234 characters. There is still scope to decrease character count.
////////////////////////////////////////

B=p=>{for(a=[],o='',d=I=0;i=p[I];I++){[_=>d++,_=>d--,_=>a[d]=(a[d]||0)+1,_=>a[d]=(a[d]||0)-1,_=>o+=(a[d]||0)+'\n',_=>a[d]=+prompt(),_=>{if(!a[d])while(p[I]!=']')I++},_=>{if(a[d])while(p[I]!='[')I--}]['><+-.,[]'.indexOf(i)]()}return o}

// You can run a program as follows.
// This program takes two numbers as input, adds them together then outputs them.
B(',>,<[->+<]>.')