# How do I round a number in JavaScript?

While working on a project, I came across a JS-script created by a former employee that basically creates a report in the form of

``````Name : Value
Name2 : Value2
``````

etc.

The peoblem is that the values can sometimes be floats (with different precision), integers, or even in the form `2.20011E+17`. What I want to output are pure integers. I don't know a lot of JavaScript, though. How would I go about writing a method that takes these sometimes-floats and makes them integers? You hav to convert your input into a number and then round them:

``````function toInteger(number){
return Math.round(  // round to nearest integer
Number(number)    // type cast your input
);
};
``````

Or as a one liner:

``````function toInt(n){ return Math.round(Number(n)); };
``````

Testing with different values:

``````toInteger(2.5);           // 3
toInteger(1000);          // 1000
toInteger("12345.12345"); // 12345
toInteger("2.20011E+17"); // 220011000000000000
`````` If you need to round to a certain number of digits use the following function

``````function roundNumber(number, digits) {
var multiple = Math.pow(10, digits);
var rndedNum = Math.round(number * multiple) / multiple;
return rndedNum;
}
`````` Here is a way to be able to use `Math.round()` with a second argument (number of decimals for rounding):

``````// 'improve' Math.round() to support a second argument
var _round = Math.round;
Math.round = function(number, decimals /* optional, default 0 */)
{
if (arguments.length == 1)
return _round(number);

var multiplier = Math.pow(10, decimals);
return _round(number * multiplier) / multiplier;
}

// examples
Math.round('123.4567', 2); // => 123.46
Math.round('123.4567');    // => 123
`````` A very good approximation for rounding:

``````function Rounding (number, precision){

var newNumber;
var sNumber = number.toString();

var increase = precision + sNumber.length - sNumber.indexOf('.') + 1;

if (number < 0)
newNumber = (number -  5 * Math.pow(10,-increase));
else
newNumber = (number +  5 * Math.pow(10,-increase));

var multiple = Math.pow(10,precision);

return Math.round(newNumber * multiple)/multiple;
}
``````

Only in some cases when the length of the decimal part of the number is very long will it be incorrect. Math.floor(19.5) = 19 should also work. According to the ECMAScript specification, numbers in JavaScript are represented only by the double-precision 64-bit format IEEE 754. Hence there is not really an integer type in JavaScript.

Regarding the rounding of these numbers, there are a number of ways you can achieve this. The Math object gives us three rounding methods wich we can use:

The Math.round() is most commonly used, it returns the value rounded to the nearest integer. Then there is the Math.floor() wich returns the largest integer less than or equal to a number. Lastly we have the Math.ceil() function that returns the smallest integer greater than or equal to a number.

There is also the toFixed() that returns a string representing the number using fixed-point notation.

Ps.: There is no 2nd argument in the Math.round() method. The toFixed() is not IE specific, its within the ECMAScript specification aswell You can also use `toFixed(x)` or `toPrecision(x)` where x is the number of digits.

Both these methods are supported in all major browsers You can use Math.round() for rounding numbers to the nearest integer.

``````Math.round(532.24) => 532
``````

Also, you can use parseInt() and parseFloat() to cast a variable to a certain type, in this case integer and floating point.