user147930

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• Math.round() doesn't follow specification for exact 0.5

  in JavaScript • 2 years, 4 months

  

  It seems like Math.round() is a better solution, but it is not! In some cases it will NOT round correctly. Also, toFixed() will NOT round correctly in some cases.

  To correct the rounding problem with the previous Math.round() and toFixed(), you can define a custom JavaScript round function that performs a "nearly equal" test to determine whether a fractional value is sufficiently close to a midpoint value to be subject to midpoint rounding. The following function return the value of the given number rounded to the nearest integer accurately.

  Number.prototype.roundTo = function(decimal) {
  return +(Math.round(this + "e+" + decimal) + "e-" + decimal);
  }

  var num = 9.7654;
  console.log( num.roundTo(2)); //output 9.77