Converting a number to two decimal places

Question

I have a number

num = 0.99922312

I would like to shorten it to just 0.99. I thought I could do this with a simple toFixed

num.toFixed(2)

However this just returns the value of 1.00. I've also tried a bunch of decimal combinations such as .toFixed(2.2) and so on.

Can anyone point me in the right direction please?

Kind of I guess but seems such a backwards way. I would need to convert the number to a string, slice it, and then back to a number again? Fair dos. Thanks for your advice. — alienbuild, May 19 '20 at 21:32
`toFixed` creates a string too. Why are you truncating it if not for purposes of displaying it? Only thing that comes to mind is currency calculations but you should be using a specialized library for that. — John Montgomery, May 19 '20 at 21:33
@JohnMontgomery Thanks, I didn't actually realise that toFixed also created a string. It's tensorflow prediction results that I'm getting from the back end and then sorting in react front end by the prediction number. The number is also displayed. — alienbuild, May 19 '20 at 21:35

Pablo CG · Answer 1 · 2020-05-19T21:32:04.453

0

This is the easiest way:

var num = 0.99922312
var twoDecimals = num.toString().substring(0, 4)
console.log(twoDecimals)

edited May 19 '20 at 21:32

answered May 19 '20 at 21:30

Pablo CG

818
6
18

Don't use `new` for primitive types. – John Montgomery May 19 '20 at 21:31
1

This approach is non-generalized: `num = 1234.56` -> `1234` (0 decimals), `num = 123.456` -> `123.` (0 decimals, dangling dot), `num = 12345` -> `1234` (oops) etc. – user2864740 May 19 '20 at 22:02

Unmitigated · Accepted Answer · 2020-05-19T21:41:15.363

You can simply convert the number to a string, get the index of the decimal point, and use slice to remove all the characters after the first two characters after the decimal point.

function truncate(num){
    var str = num.toString();
    var idx = str.indexOf('.');
    return idx != -1 ? str.slice(0, idx + 3): str;
}
console.log(0.99922312, "->", truncate(0.99922312));
console.log(0.8, "->", truncate(0.8));
console.log(0.121, "->", truncate(0.121));
console.log(0.235, "->", truncate(0.235));
console.log(12, "->", truncate(12));

If you need the truncated result as a number instead of a string, you can use the unary plus operator to convert it back to a number.

var truncatedNum = +truncate(num);

Converting a number to two decimal places

2 Answers2