Number.prototype.toPrecision()

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This feature is well established and works across many devices and browser versions. Its been available across browsers since July 2015.

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The toPrecision() method of Number values returns a string representing this number to the specified number of significant digits.

Try it

function precise(x) {
  return x.toPrecision(4);
}

console.log(precise(123.456));
// Expected output: "123.5"

console.log(precise(0.004));
// Expected output: "0.004000"

console.log(precise(1.23e5));
// Expected output: "1.230e+5"

Syntax

toPrecision()
toPrecision(precision)

Parameters

precision Optional: An integer specifying the number of significant digits.

A string representing the given number, using the given number of significant digits. Scientific notation is used if the exponent is greater than or equal to precision or less than -6. Has the same behavior as Number.prototype.toString() if the precision argument is omitted.

Exceptions

RangeError: Thrown if precision is not between 1 and 100 (inclusive).
TypeError: Thrown if this method is invoked on an object that is not a Number.

Examples

Using `toPrecision`

// This number has exponent 0, so it will never use exponential notation
let num = 5.123456;

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

// This number has exponent -4, so it will never use exponential notation
num = 0.000123;

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

// This number has exponent 3, so it will use exponential notation if precision is less than 4
num = 1234.5;
console.log(num.toPrecision(1)); // '1e+3'
console.log(num.toPrecision(2)); // '1.2e+3'
console.log(num.toPrecision(6)); // '1234.50'

// This number has exponent -7, so it will always use exponential notation
num = 0.00000012345;
console.log(num.toPrecision(1)); // '1e-7'
console.log(num.toPrecision(10)); // '1.234500000e-7'