JavaScript: The Definitive Guide, 6th Edition

Name

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

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()