brainfuck interpreter

brainfuck.js

class Brainfuck {
  memory = new Uint8Array(30000);
  ptr = 0;
  input = { read() { return 0 } };
  output = { write(v) { console.log(String.fromCharCode(v)) } };
  run(code) {
    for (let i = 0, len = code.length; i < len; ++i) {
      let c = code.charAt(i);
      switch (c) {
        // move pointer right
        case '>': this.ptr += 1; break;
        // move point left
        case '<': this.ptr -= 1; break;
        // increment cell
        case '+': this.memory[this.ptr] += 1; break;
        // decrement cell
        case '-': this.memory[this.ptr] -= 1; break;
        // write cell to output
        case '.': this.output.write(this.memory[this.ptr]); break;
        // read to cell from output
        case ',': this.memory[this.ptr] = this.input.read(); break;
        // jump to next `]` if cell is 0
        case '[': if (this.memory[this.ptr] === 0) {
          while (i !== len - 1 && code.charAt(i++) !== ']');
        } break;
        // jump to previous `[` if cell is not 0
        case ']': if (this.memory[this.ptr] !== 0) {
          while (i !== 0 && code.charAt(--i) !== '[');
        } break;
        // ignore all other characters
        default: break;
      }
    }
  }
  reset() {
    for (let i = 0, len = this.memory.length; i < len; ++i) {
      this.memory[i] = 0;
    }
    this.ptr = 0;
  }
}

let vm = new Brainfuck;

vm.run(`
++       Cell c0 = 2
> +++++  Cell c1 = 5

[        Start your loops with your cell pointer on the loop counter (c1 in our case)
< +      Add 1 to c0
> -      Subtract 1 from c1
]        End your loops with the cell pointer on the loop counter

At this point our program has added 5 to 2 leaving 7 in c0 and 0 in c1
but we cannot output this value to the terminal since it is not ASCII encoded

To display the ASCII character "7" we must add 48 to the value 7
We use a loop to compute 48 = 6 * 8

++++ ++++  c1 = 8 and this will be our loop counter again
[
< +++ +++  Add 6 to c0
> -        Subtract 1 from c1
]
< .        Print out c0 which has the value 55 which translates to "7"!
`);