How do I round a number in javascript?

Question

Hey all.

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...

Problem for me though, is that the values can sometimes be floats (with different precision), integers, or even in the form "2.20011E+17"

What I outputted though 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?

Answer 1

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.

Answer 2

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

Answer 3

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

Answer 4

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;
        }