CODEWITHSUNDEEP
javascriptmathrounding
core4096
core4096

Reputation: 111

Javascript: how to round number to 2 non-zero decimals

Without jQuery, how can I round a float number to 2 non-zero decimals (but only when needed - 1.5 instead of 1.50)?

Just like this:

2.50000000004 -> 2.5
2.652 -> 2.65
2.655 -> 2.66
0.00000204 -> 0.000002
0.00000205 -> 0.0000021

I tried this code:

var r = n.toFixed(1-Math.floor(Math.log10(n)));

but n=0.00000205 implies r=0.0000020, which is in conflict with conditions above. But n=0.0000020501 implies r=0.0000021, which is OK, so the error is only for 5 as a last decimal, which should be rounded up.

Upvotes: 2

Views: 2196

Answers (2)

sergis4ake
sergis4ake

Reputation: 21

Thank's for the @Arnauld answer. Just added decimals parameter.

function roundToDecimals(n, decimals) {
  var log10 = n ? Math.floor(Math.log10(n)) : 0,
      div = log10 < 0 ? Math.pow(10, decimals - log10 - 1) : Math.pow(10, decimals);

  return Math.round(n * div) / div;
}

var numDecimals = 2
var test = [
  2.50000000004,
  2.652,
  2.655,
  0.00000204,
  0.00000205,
  0.00000605
];

test.forEach(function(n) {
  console.log(n, '->', roundToDecimals(n, numDecimals));
});

Upvotes: 0

Arnauld
Arnauld

Reputation: 6110

This should do what you want:

function twoDecimals(n) {
  var log10 = n ? Math.floor(Math.log10(n)) : 0,
      div = log10 < 0 ? Math.pow(10, 1 - log10) : 100;

  return Math.round(n * div) / div;
}

var test = [
  2.50000000004,
  2.652,
  2.655,
  0.00000204,
  0.00000205,
  0.00000605
];

test.forEach(function(n) {
  console.log(n, '->', twoDecimals(n));
});

Upvotes: 8

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