How to replace characters recursively within a string

Question

I have a mathematical expression that does exponentials (e.g. 2 Raised to the power of 2) which I normally pass to the JavaScript eval function. An example of my string expression is 2^2^2. Now, JavaScript doesn't have an exponential operator so in the current example the operator you see between the operands is a bitwise operator in JavaScript.

What I try to do is to replace the string that matches the pattern d1 ^ d2 with the value returned from Math.pow (d1, d2). Now, it does this successfully for the first occurence but doesn't do it for other occurrences. Below is my code:

var str = '2^2^2';
var regex = /(\d+)\^(\d+)/g;

str = str.replace(c, function(match, $1, $2) {
    console.log(match + '---' + $1 + '---' + $2);
    return Math.pow($1,$2);
});
console.log(str);

eval(str);

Anytime I log the ouput of str it gives 4^2 instead of 16 and so I always get the wrong answer after the eval function actions. Please does anyone have any idea how I can go about solving this problem.

Your regex is quite simple, it fails with a number of cases: non integer numbers (2.3^2), numbers with exp (2e-3^0.5), negative numbers (2^-2, 4+-5^2) — Nick Rassadin, Apr 15 '16 at 08:49

score 2 · Accepted Answer · edited Apr 15 '16 at 08:35

2

You could use a recursive function that stops when no other token was matched. For example:

var str = '2^2^2';
var regex = /(\d+)\^(\d+)/g;

function recursive(str) {
  var matched = false;
  str = str.replace(regex, function(match, $1, $2) {
    if (match) {
      matched = true;
    }
    return Math.pow($1, $2);
  });
  if (matched) {
    str = recursive(str);
  }
  return str;
}

var result = recursive(str);
console.log(result);

<script src="http://gh-canon.github.io/stack-snippet-console/console.min.js"></script>

edited Apr 15 '16 at 08:35

Tushar

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answered Apr 15 '16 at 08:32

Lulylulu

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@Tushar do u have any idea how i can write the regex such that the replace works for negative, positive and decimal numbers? Thanks – user3775998 Apr 15 '16 at 09:57

How to replace characters recursively within a string

1 Answers1