JavaScript: The Definitive Guide, Fourth Edition

Name

Number.toPrecision( ) — format the significant digits of a number

Availability

JavaScript 1.5; JScript 5.5, ECMAScript v3

Synopsis

                  number.toPrecision(precision)

Arguments

precision

The number of significant digits to appear in the returned string. This may be a value between 1 and 21, inclusive. Implementations are allowed to optionally support larger and smaller values of precision. If this argument is omitted, the toString( ) method is used instead to convert the number to a base-10 value.

Returns

A string representation of number that contains precision significant digits. If precision is large enough to include all the digits of the integer part of number, the returned string uses fixed-point notation. Otherwise, exponential notation is used with one digit before the decimal place and precision -1 digits after the decimal place. The number is rounded or padded with zeros as necessary.

Throws

RangeError

If digits is too small or too large. Values between 1 and 21, inclusive, will not cause a RangeError. Implementations are allowed to support larger and smaller values as well.

TypeError

If this method is invoked on an object that is not a Number.

Example

var n = 12345.6789;
n.toPrecision(1);   // Returns 1e+4
n.toPrecision(3);   // Returns 1.23e+4
n.toPrecision(5);   // Returns 12346: note rounding
n.toPrecision(10);  // Returns 12345.67890: note added zero

See Also

Number.toExponential( ), Number.toFixed( ), Number.toLocaleString( ), Number.toString( )