Rounding the result of division in Javascript

Question

I'm performing the following operation in Javascript:

0.0030 / 0.031

How can I round the result to an arbitrary number of places? What's the maximum number that a var will hold?

Answer 1

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.

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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.
2. Apply Math.round()
3. 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

Answer 2

The largest positive finite value of the number type is approximately 1.7976931348623157 * 10³⁰⁸. ECMAScript-262 3rd ed. also defines Number.MAX_VALUE which holds that value.

Answer 3

To answer Jag's questions:

1. Use the toFixed() method. Beware; it returns a string, not a number.
2. Fifteen, maybe sixteen. If you try to get more, the extra digits will be either zeros or garbage. Try formatting something like 1/3 to see what I mean.