Using Math.floor() is one way of doing this.

More information: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/floor

Modern browsers should support a method called toFixed(). Here's an example taken from the web:

// Example: toFixed(2) when the number has no decimal places
// It will add trailing zeros
var num = 10;
var result = num.toFixed(2); // result will equal 10.00

// Example: toFixed(3) when the number has decimal places
// It will round to the thousandths place
num = 930.9805;
result = num.toFixed(3); // result will equal 930.981

toPrecision() might also be useful for you, there is another excellent example on that page.

For older browsers, you can achieve it manually using Math.round. Math.round() will round to the nearest integer. In order to achieve decimal precision, you need to manipulate your numbers a bit:

1. Multiply the original number by 10^x (10 to the power of x), where x is the number of decimal places you want.
   • Apply Math.round()
   • Divide by 10^x

So to round 5.11111111 to three decimal places, you would do this:

var result=Math.round(5.111111*1000)/1000  //returns 5.111