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 m not sure how to go about just dropping the decimal and everything past it  as it doesn t seem like JavaScript has a substr function like PHP does   Any recommendations

User · Answer

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.

User · Answer

Math trunc   function removes all the fractional digits   For positive number it behaves exactly the same as Math floor     console log Math trunc 89 13349       output is 89   For negative numbers it behaves same as Math ceil     console log Math trunc -89 13349      output is -89

User · Answer

I ll add my solution here   We can use floor when values are above 0 and ceil when they are less than zero  function truncateToInt x        if x  gt  0                 return Math floor x             else                return Math ceil x             Then  y   truncateToInt 2 9999      results in 2 y   truncateToInt -3 118     results in -3  Notice  This answer was written when Math trunc x  was fairly new and not supported by a lot of browsers   Today  modern browsers support Math trunc x

User · Answer

If you have a string  parse it as an integer   var num    20 536   var result   parseInt num  10       20   If you have a number  ECMAScript 6 offers Math trunc for completely consistent truncation  already available in Firefox 24  and Edge   var num   -2147483649 536  var result   Math trunc num       -2147483649   If you can   t rely on that and will always have a positive number  you can of course just use Math floor   var num   20 536  var result   Math floor num       20   And finally  if you have a number in   minus 2147483648  2147483647   you can truncate to 32 bits using any bitwise operator    0 is common  and  gt  gt  gt  0 can be used to obtain an unsigned 32-bit integer   var num   -20 536  var result   num   0      -20

User · Answer

Travis Pessetto s answer along with mozey s trunc2 function were the only correct answers  considering how JavaScript represents very small or very large floating point numbers in scientific notation   For example  parseInt -2 2043642353916286e-15  will not correctly parse that input  Instead of returning 0 it will return -2   This is the correct  and imho the least insane  way to do it   function truncate number        return number  gt  0            Math floor number             Math ceil number

User · Answer

Use Math floor     var f   20 536  var i   Math floor f       20   http   jsfiddle net J4UVV 1

[javascript] Truncate/round whole number in JavaScript?

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