How to make the precision of float numbers the same using Javascript

Question

I have two float numbers in Javascript with high and lower precision (not known in advance) for example:

1545.165 
12.15364613

How can I round the high precision number to the same precision as lower precision number? In our case to

12.154

Answer 1

You can wrangle around with the toFixed() function.

Syntax: <number>.toFixed(precision)

For example:

12.15364613.toFixed(3) gives 12.154

But to make it work in your case you want to do something like this:

Warning untested code, I only meant to give you a general idea of how this can be done, of course the code below can be improved.

var num1 = 12.15364613;
var num1Str = (12.15364613).toString();
var num1Precision = parseInt(num1Str.substring(num1Str.indexOf('.')).length - 1);
var num2 = 12.154;
var num2Str = (12.154).toString();
var num2Precision = parseInt(num2Str.substring(num2Str.indexOf('.')).length - 1);
if(num1Precision > num2Precision){
 num1 = num1.toFixed(num2Precision);
} else{
 num2 = num2.toFixed(num1Precision);
}

• Филипп Цветков: How do you know that precision is equal to 3 ?
• Kroltan: @ФилиппЦветков You choose what precision you find useful.
• Michelangelo: @Kroltan I think OP means something else with precision, but I also don't know what.
• Филипп Цветков: The precision is not known in advance. I put the precise numbers as examples
• Филипп Цветков: Better. But there is no any native number function to get precision without converting it to string?

Answer 2

Pure Math Solution

In order to get precision of unknown number (variable) you can use such a function:

function getPrecision(x) {
 // i < 10 - just to avoid infinite looping
 // (which may occur if x is a real number like PI)
 // x - Math.floor(x) + (x < 0? 1 : 0) is a fractional part of x
 for (var i = 0; i < 10 && x - Math.floor(x) + (x < 0? 1 : 0) > 0; i++, x *= 10) ;
 return i;
}

So the code should like this:

// array of given numbers:
aVals = [1545.165, 12.15364613];
// array of numbers' precisions:
var aPre = aVals.map(getPrecision);
// find the least precision:
var minPre = Math.min.apply(null, aPre);
// result array of fixed numbers with the same precision:
var aValsFixed = aVals.map(function(v) { return v.toFixed(minPre); });

Answer 3

You mean something like this?

var number = 1.2333445454;
var n = number.toFixed(3);
alert(n);

• Филипп Цветков: Why you fixed precision to 3?
• Филипп Цветков: The precision is not known in advance. I put the precise numbers as examples