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toExponential

The

toFixed()

method returns a string representation of a number with a specified number of decimal

points. For example:

var oNumberObject = new Number(99);

alert(oNumberObject.toFixed(2)); //outputs “99.00”

Here, the

toFixed()

method is given an argument of

, which indicates how many decimal places

should be displayed. As a result, the method returns the string

“99.00”

, filling out the empty decimal

places with 0s. This method can be very useful for applications dealing with currency. The

toFixed()

method can represent numbers with 0 to 20 decimal places; other values may cause errors.

Another method related to formatting numbers is the

toExponential()

method, which returns a string

with the number formatted in e-notation. Just as with

toFixed()

toExponential()

accepts one argu-

ment, which is the number of decimal places to output. For example:

var oNumberObject = new Number(99);

alert(oNumberObject.toExponential(1)); //outputs “9.9e+1”

This code outputs

“9.9e+1”

as the result, which you may remember from the earlier explanation, repre-

sents 9.9 x 10

. The question is, what if you don’t know the proper format to use for a number: fixed or

exponential? That’s where the

toPrecision()

method comes in.

The

toPrecision()

method returns either the fixed or exponential representation of a number, depend-

ing on which makes the most sense. This method takes one argument, which is the total number of digits

to use to represent the number (not including exponents). Example:

var oNumberObject = new Number(99);

alert(oNumberObject.toPrecision(1)); //outputs “1e+2”

In this example, the task is to represent the number

with a single digit, which results in

“1e+2”

, oth-

erwise known as 100. Yes,

toPrecision()

rounded the number to get as close as possible to the actual

value. Because you can’t represent 99 with any fewer than 2 digits, this rounding had to occur. If, how-

ever, you want to represent 99 using two digits, well, that’s easy:

var oNumberObject = new Number(99);

alert(oNumberObject.toPrecision(2)); //outputs “99”

Of course the output is

“99”

, because that is the exact representation of the number. But what if you

specify more than the number of digits needed?

var oNumberObject = new Number(99);

alert(oNumberObject.toPrecision(3)); //outputs “99.0”

In this case,

toPrecision(3)

is exactly equivalent to

toFixed(1)

, outputting

“99.0”

as the result.

The

toFixed(), toExponential()

, and

toPrecision()

methods round up or down to accu-

rately represent a number with the correct number of decimal places.

Chapter 2

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