How do you convert numbers between different bases in JavaScript?

Solution 1:

The API

To convert to a number from a hex string:

parseInt(string, radix)

• string: Required. The string to be parsed

• radix: Optional. A number (from 2 to 36) that represents the numeral system to be used

To convert from a number to a hex string:

NumberObject.toString(radix)

• radix: Optional. Specifies the base radix you would like the number displayed as.

Example radix values:

• 2 - The number will show as a binary value
• 8 - The number will show as an octal value
• 16 - The number will show as an hexadecimal value

Example Usage

Integer value to hex:

var i = 10;
console.log( i.toString(16) );

Hex string to integer value:

var h = "a";
console.log( parseInt(h, 16) );

Integer value to decimal:

 var d = 16;
 console.log( d.toString(10) );

Solution 2:

I came to this post needing to convert from base 10 to 62 and vice-versa. Whilst the solutions here are great, parseInt and toString only support base 2 to 36. So if anyone finds themselves in a similar position to me needing base 2 to 62, I've pasted my solution below.

https://gist.github.com/ryansmith94/91d7fd30710264affeb9

function convertBase(value, from_base, to_base) {
  var range = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+/'.split('');
  var from_range = range.slice(0, from_base);
  var to_range = range.slice(0, to_base);
  
  var dec_value = value.split('').reverse().reduce(function (carry, digit, index) {
    if (from_range.indexOf(digit) === -1) throw new Error('Invalid digit `'+digit+'` for base '+from_base+'.');
    return carry += from_range.indexOf(digit) * (Math.pow(from_base, index));
  }, 0);
  
  var new_value = '';
  while (dec_value > 0) {
    new_value = to_range[dec_value % to_base] + new_value;
    dec_value = (dec_value - (dec_value % to_base)) / to_base;
  }
  return new_value || '0';
}