better_to_fixed.js

/*jslint indent: 2 */
/* toFixed converts the input to a number and returns it rounded to 2 decimal places */
/* For a deeper insight on javascript numbers, read http://ecma-international.org/ecma-262/5.1/#sec-8.5 */
function toFixed(val) {
  'use strict';
  var floatError = 1000000,                  /* floating point errors less than (1/floatError) == 0.000001 will be corrected */
    decRound = 100,                          /* the result is rounded to integer multiples of (1/decRound) == 0.01 */
    n = parseFloat(val),                     /* convert input to floating point number */
    sign = n < 0 ? '-' : '',                 /* sign of the given input */
    intFrac,                                 /* integer and fractional parts of a decimal number */
    int,                                     /* integer part of a decimal number */
    frac,                                    /* fractional part of a decimal number */
    result,                                  /* absolute result as floating point number */
    roundCorrection = floatError / decRound; /* correct rounding offset between floatError and decRound */

  result = Math.round(Math.abs(n) * floatError) / roundCorrection; /* result without floating point errors */
  result = Math.round(result) / decRound;                          /* rounded result */

  intFrac = result.toString().split('.');
  int = intFrac[0];
  frac = ((intFrac[1] || '00') + '0').substr(0, 2);

  return sign + int + '.' + frac;
}

/*
toFixed() is implemented to deal with real world monetary calculations 
toFixed() fixes float rounding errors smaller than 0.000001
toFixed() will fail when dealing with numbers greater than 1000000000
Don't use this implementation, if you want to deal with numbers
  * greater than 1000000000 or
  * less than 0.000001
*/

toFixed(0);                     /*            "0.00" */
toFixed(1.5);                   /*            "1.50" */
toFixed('3.5.1');               /*            "3.50" */
toFixed(0.29 + 0.03);           /*            "0.32" */
toFixed(0.2 * 17.5 / 100);      /*            "0.04" */
toFixed(0.24499999999999995);   /*            "0.25" (assume floating point error) */
toFixed(-0.24499999999999995);  /*           "-0.25" (assume floating point error) */
toFixed(0.014994);              /*            "0.01" */
toFixed(0.014995);              /*            "0.01" */
toFixed(0.0149994);             /*            "0.01" */
toFixed(0.0149995);             /*            "0.02" */
toFixed(0.01499994);            /*            "0.02" (assume floating point error) */
toFixed(0.01499995);            /*            "0.02" (assume floating point error) */
toFixed(1000000000.014999);     /*   "1000000000.01" */
toFixed(10000000000.014999);    /*  "10000000000.02" (unavoidable error case, number too large) */
toFixed(1000000000.0149999);    /*   "1000000000.02" (assume floating point error) */