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How can I round down a number in Javascript?

Asked 2009-09-16T23:06:42.320
288

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 a better way of doing it other than breaking it apart at the decimal point at keeping the first bit. There must be...

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2 Answers

42

Math.floor() will work, but it's very slow compared to using a bitwise OR operation:

var rounded = 34.923 | 0;
alert( rounded );
//alerts "34"

EDIT Math.floor() is not slower than using the | operator. Thanks to Jason S for checking my work.

Here's the code I used to test:

var a = [];
var time = new Date().getTime();
for( i = 0; i < 100000; i++ ) {
    //a.push( Math.random() * 100000  | 0 );
    a.push( Math.floor( Math.random() * 100000 ) );
}
var elapsed = new Date().getTime() - time;
alert( "elapsed time: " + elapsed );
answered 2009-09-16T23:15:47.717
8
Math.floor(1+7/8)
answered 2009-09-16T23:14:02.193

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