Round Half To Even With Javascript

Updated: v0.2.1

(special thanks to: Donatas v0.2.0 (http://happycode.info)

The following script provides an easy way to perform unbiased rounding, convergent rounding, statistician's rounding, Dutch rounding, Gaussian rounding, or bankers' rounding using Javascript.

Examples

var numToRound = 10.005;
numToRound.rhte(0.01);
result: 10.00

var numToRound = 10.0015;
numToRound.rhte(0.001);
result: 10.002

var numToRound = 10.00500000001;
numToRound.rhte(0.01);
result: 10.01

var numToRound = 1005001;
numToRound.rhte(10000);
result: 1010000

/*
  Round Half To Even (rhte) extends the 'Number' and 'String' objects
  Argument(placeToRound) examples: 0.0001,0.01,1,10,100
  Usage:
    Number.rhte(rounding value)
      (124.34450000).rhte(0.001) - [Result: 124.344]
      (124.34450001).rhte(0.001) - [Result: 124.345]
      (124.34550000).rhte(0.001) - [Result: 124.346]
    String.rhte(rounding value)
      '124.34450000'.rhte(0.001) - [Result: 124.344]
      '124.34450001'.rhte(0.001) - [Result: 124.345]
      '124.34550000'.rhte(0.001) - [Result: 124.346]
*/
var rhte = function(placeToRound){
  var fixed = placeToRound.toString().split('.').length < 2 ? 0 : placeToRound.toString().split('.')[1].length,
  numParts = {
    mvDec : (this/placeToRound).toFixed(this.toString().length).toString().split('.'),
    wholeNum: function(){return parseInt(this.mvDec[0],10);},
    dec: function(){return this.mvDec.length > 1 ? parseFloat('0.'+this.mvDec[1]) : 0;},
    oddEven: function(){return (this.wholeNum() % 2 === 1) ? 1 : 0;}
  };
      
  if(numParts.dec() !== 0.5){
    return(numParts.dec() > 0.5) ? parseFloat(((numParts.wholeNum()+1)*placeToRound).toFixed(fixed)) : parseFloat((numParts.wholeNum()*placeToRound).toFixed(fixed));
  }
  else{
    if(numParts.oddEven() === 1){
      return parseFloat(((numParts.wholeNum()+1)*placeToRound).toFixed(fixed));
    }
    else{
      return parseFloat((numParts.wholeNum()*placeToRound).toFixed(fixed));
    }
  }
};
Number.prototype.rhte = rhte;
String.prototype.rhte = rhte;

test("Unit Tests", function() { //QUnit Tests
  ok( (1.000).rhte(1) === 1, "(1.000).rhte(1) === 1" );
  ok( ('1.000').rhte(1) === 1, "('1.000').rhte(1) === 1" );
  ok( (1.01).rhte(0.001) === 1.010, "(1.01).rhte(0.001) === 1.010" );
  ok( (10.0501).rhte(0.1) === 10.1, "(10.0501).rhte(0.1) === 10.1" );
  ok( (1.01499999).rhte("0.01") === 1.01, "(1.01499999).rhte(\"0.01\") === 1.01" );
  ok( (1.0150000000).rhte(0.01) === 1.02, "(1.0150000000).rhte(0.01) === 1.02" );
  ok( (476).rhte(50) === 500, "(476).rhte(50) === 500" );
});

<html> Result:

Run

This entry was posted on Monday, November 30th, 2009 at 8:19 pm and is filed under Financial, Web. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.

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