number.toPrecision

The toPrecision() method returns a string representing the Number object to the specified precision.

Syntax

numObj.toPrecision([precision])

Parameters

precision

Optional. An integer specifying the number of significant digits.

Return value

A string representing a Number object in fixed-point or exponential notation rounded to precision significant digits. See the discussion of rounding in the description of the Number.prototype.toFixed() method, which also applies to toPrecision().

If the precision argument is omitted, behaves as Number.prototype.toString(). If the precision argument is a non-integer value, it is rounded to the nearest integer.

Exceptions

RangeError

If precison is not between 1 and 100 (inclusive), a RangeError is thrown. Implementations are allowed to support larger and smaller values as well. ECMA-262 only requires a precision of up to 21 significant digits.

Examples

Using toPrecision

var numObj = 5.123456;

console.log(numObj.toPrecision());    // logs '5.123456'
console.log(numObj.toPrecision(5));   // logs '5.1235'
console.log(numObj.toPrecision(2));   // logs '5.1'
console.log(numObj.toPrecision(1));   // logs '5'

numObj = 0.000123

console.log(numObj.toPrecision());    // logs '0.000123'
console.log(numObj.toPrecision(5));   // logs '0.00012300'
console.log(numObj.toPrecision(2));   // logs '0.00012'
console.log(numObj.toPrecision(1));   // logs '0.0001' 

// note that exponential notation might be returned in some circumstances
console.log((1234.5).toPrecision(2)); // logs '1.2e+3'

Specifications

Specification	Status	Comment
ECMAScript 3rd Edition (ECMA-262)	Standard	Initial definition. Implemented in JavaScript 1.5.
ECMAScript 5.1 (ECMA-262) The definition of 'Number.prototype.toPrecision' in that specification.	Standard
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Number.prototype.toPrecision' in that specification.	Standard
ECMAScript 2017 Draft (ECMA-262) The definition of 'Number.prototype.toPrecision' in that specification.	Draft

Browser compatibility

See also

• Number.prototype.toFixed()
• Number.prototype.toExponential()
• Number.prototype.toString()