Truncate/round whole number in JavaScript?

Question

For a script I\'m writing, I need display a number that has been rounded, but not the decimal or anything past it. I\'ve gotten down to rounding it to the third place, but I

Answer 1

Convert the number to a string and throw away everything after the decimal.

trunc = function(n) { return Number(String(n).replace(/\..*/, "")) }

trunc(-1.5) === -1

trunc(1.5) === 1

Edit 2013-07-10

As pointed out by minitech and on second thought the string method does seem a bit excessive. So comparing the various methods listed here and elsewhere:

function trunc1(n){ return parseInt(n, 10); }
function trunc2(n){ return n - n % 1; }
function trunc3(n) { return Math[n > 0 ? "floor" : "ceil"](n); }
function trunc4(n) { return Number(String(n).replace(/\..*/, "")); }

function getRandomNumber() { return Math.random() * 10; }

function test(func, desc) {
    var t1, t2;
    var ave = 0;
    for (var k = 0; k < 10; k++) {
        t1 = new Date().getTime();
        for (var i = 0; i < 1000000; i++) {
            window[func](getRandomNumber());
        }
        t2 = new Date().getTime();
        ave += t2 - t1;
    }
    console.info(desc + " => " + (ave / 10));
}

test("trunc1", "parseInt");
test("trunc2", "mod");
test("trunc3", "Math");
test("trunc4", "String");

The results, which may vary based on the hardware, are as follows:

parseInt => 258.7
mod      => 246.2
Math     => 243.8
String   => 1373.1

The Math.floor / ceil method being marginally faster than parseInt and mod. String does perform poorly compared to the other methods.