Formatting numbers for currency display and more.
Using it, any supplied argument is rounded off to the nearest integer, and using the ".5" up rule. For example:
Math.round(25.9) //returns 26
Math.round(25.2) //returns 25
Math.round(-2.58) //returns -3
If purging numbers of decimals is all that you require, class dismissed!
Taking things a few decimal further
Formatting numbers to specific decimal points still entails Math.round(), but padded with a little multiplication and division. See if you can identify the magic formula involved, with the below examples:
1) //round "original" to two decimals
var result=Math.round(original*100)/100 //returns 28.45
2) // round "original" to 1 decimal
var result=Math.round(original*10)/10 //returns 28.5
3) //round 8.111111 to 3 decimals
var result=Math.round(8.111111*1000)/1000 //returns 8.111
In case you haven't picked up on it, the formula to round any number to x decimal points is:
1) Multiple the original number by 10^x (10 to the power of x)
2) Apply Math.round() to the result
3) Divide result by 10^x
Formatting numbers for currency display
Number.toFixed(x) - Formats any number for "x" number of trailing decimals. The number is rounded up, and "0"s are used after the decimal point if needed to create the desired decimal length.
Number.toPrecision(x) - Formats any number so it is of "x" length. Also called significant digits. A decimal point and "0"s are used if needed to create the desired length.
The best way to see all the subtleties of toFixed() is to see it in action:
profits.toFixed(3) //returns 2489.824 (round up)
profits.toFixed(2) //returns 2489.82
profits.toFixed(7) //returns 2489.8237000 (padding)
Displaying any number in currency format can't get any easier!
To toPrecision() now:
anumber.toPrecision(6) //returns 123.450 (padding)
anumber.toPrecision(4) //returns 123.5 (round up)
anumber.toPrecision(2) //returns 1.2e+2 (you figure it out!)
toPrecision() is useful if your number must be of a certain length.
if (profits.toFixed) //if browser supports toFixed() method
For those of you who also need to ensure legacy browsers such as IE5 also perform the desired number formatting operation, well, then it's time to roll your own function.