How do you write an arithmetic expression parser in JavaScript, without using eval or a constructor function?

Question

Given a string:

 var str1 = \"25*5+5*7\";

Without using eval or the constructor function in JavaScript, how would I be able to

Answer 1

You can create a new script:

function parse(str) {
  var s = document.createElement('script');
  s.text = "window.result = " + str;
  document.body.appendChild(s); // Run script
  document.body.removeChild(s); // Clean up
  return result;                // Return the result
}
document.body.innerHTML = parse("5*5+5*5");

Or use event handler content attributes:

function parse(str) {
  var el = document.createElement('div');
  el.setAttribute('onclick', "this.result = " + str);
  el.onclick();     // Run script
  return el.result; // Return the result
}
document.body.innerHTML = parse("5*5+5*5");

Note these approaches are unsafe and as evil as eval but uglier. So I don't recommend them.