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?

With that example, I want the function to accept '1+1' and return 2.

Answer 1

You can use the JavaScript Expression Evaluator library, which allows you to do stuff like:

Parser.evaluate("2 ^ x", { x: 3 }); 

Or mathjs, which allows stuff like:

math.eval('sin(45 deg) ^ 2'); 

I ended up choosing mathjs for one of my projects.

Answer 2

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.