How can I round down a number in Javascript?

Question

How can I round down a number in JavaScript?

math.round() doesn\'t work because it rounds it to the nearest decimal.

I\'m not sure if there is

Answer 1

Math.floor(1+7/8)

Answer 2

To round down towards negative infinity, use:

rounded=Math.floor(number);

To round down towards zero (if the number can round to a 32-bit integer between -2147483648 and 2147483647), use:

rounded=number|0;

To round down towards zero (for any number), use:

if(number>0)rounded=Math.floor(number);else rounded=Math.ceil(number);

Answer 3

You can try to use this function if you need to round down to a specific number of decimal places

function roundDown(number, decimals) {
    decimals = decimals || 0;
    return ( Math.floor( number * Math.pow(10, decimals) ) / Math.pow(10, decimals) );
}

examples

alert(roundDown(999.999999)); // 999
alert(roundDown(999.999999, 3)); // 999.999
alert(roundDown(999.999999, -1)); // 990

Answer 4

Round towards negative infinity - Math.floor()

+3.5 => +3.0
-3.5 => -4.0

Round towards zero - usually called Truncate(), but not supported by JavaScript - can be emulated by using Math.ceil() for negative numbers and Math.floor() for positive numbers.

+3.5 => +3.0 using Math.floor()
-3.5 => -3.0 using Math.ceil()

Answer 5

Was fiddling round with someone elses code today and found the following which seems rounds down as well:

var dec = 12.3453465,
int = dec >> 0; // returns 12

For more info on the Sign-propagating right shift(>>) see MDN Bitwise Operators

It took me a while to work out what this was doing :D

But as highlighted above, Math.floor() works and looks more readable in my opinion.