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.
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.
0.000020
for that is related to the imprecision of the floating point representation. 0.0000205
cannot be represented as exactly that value in floating point. For numbers that can, the result is as you would expect. NB: Ad-hoc coded functions that try to do this will probably all suffer from the same problem.
– trincot
Commented
Aug 8, 2016 at 21:40
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));
});
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));
});