integer rounding with parseInt in javascript

Question

I have the following javascript code.

if( frequencyValue <= 30)
            leftVal = 1;
        else if (frequencyValue > 270)
            leftVal= 10;
        else 
            leftVal = parseInt(frequencyValue/30);

Currently if given the value 55 (for example) it will return 1 since 1< 55/30 < 2. I was wondering if there was a way to round up to 2 if the decimal place being dropped was greater than .5.

thanks in advance

Chetan S · Accepted Answer · 2009-08-04 16:57:58Z

45

Use a combination of parseFloat and Math.round

Math.round(parseFloat("3.567")) //returns 4

[EDIT] Based on your code sample, you don't need a parseInt at all since your argument is already a number. All you need is Math.round

edited Aug 4, 2009 at 16:57

answered Aug 4, 2009 at 16:50

Chetan S

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2 Comments

Pete Duncanson Over a year ago

from painful experience I would always recommend passing in the optional second param to force it to ten base: parseInt( myNum, 10 ) otherwise you can get in a whole world of debug pain when it tries converting strings that start with 0's etc which throw it all out into Hex mode and so on, a real head hurter...!

Chetan S Over a year ago

I agree, except that parseFloat doesn't have the radix parameter. It is just parseFloat(string).

cdm9002 · Accepted Answer · 2009-08-04 17:05:57Z

7

leftVal = Math.floor(frequencyValue/30 + 0.5);

answered Aug 4, 2009 at 17:05

cdm9002

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4 Comments

C. Ross Over a year ago

This looks wrong. Floor returns the lower value always, which is specifically what the questioner didn't want.

C. Ross Over a year ago

Ah, I see. A rather hackerish way of doing it, but ok.

cdm9002 Over a year ago

Perfectly acceptable technique. This is how round is implemented. From javadoc's Math.round: "The result is rounded to an integer by adding 1/2, taking the floor of the result, and casting the result to type int".

aaaaaaaaaaaa Over a year ago

Math.round use the round to even convention, which in most cases is a bit weird, this does standard mathematical rounding.

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