Evaluating a string as a mathematical expression in JavaScript

Question

How do I parse and evaluate a mathematical expression in a string (e.g. \'1+1\') without invoking eval(string) to yield its numerical value?

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Answer 1

You can do + or - easily:

function addbits(s) {
  var total = 0,
      s = s.match(/[+\-]*(\.\d+|\d+(\.\d+)?)/g) || [];
      
  while (s.length) {
    total += parseFloat(s.shift());
  }
  return total;
}

var string = '1+23+4+5-30';
console.log(
  addbits(string)
)

More complicated math makes eval more attractive- and certainly simpler to write.