Number.prototype.toString()

BaselineWidely available

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

ThetoString() method ofNumber values returns a string representing this number value.

Try it

function hexColor(c) {  if (c < 256) {    return Math.abs(c).toString(16);  }  return 0;}console.log(hexColor(233));// Expected output: "e9"console.log(hexColor("11"));// Expected output: "b"

Syntax

toString()toString(radix)

Parameters

radixOptional: An integer in the range2 through36 specifying the base to use for representing the number value. Defaults to 10.

Return value

A string representing the specified number value. Scientific notation is used if radix is 10 and the number's magnitude (ignoring sign) is greater than or equal to 10²¹ or less than 10^-6.

Exceptions

RangeError: Thrown ifradix is less than 2 or greater than 36.
TypeError: Thrown if this method is invoked on an object that is not aNumber.

TheNumber object overrides thetoString method ofObject; it does not inheritObject.prototype.toString(). ForNumber values, thetoString method returns a string representation of the value in the specified radix.

For radixes above 10, the letters of the alphabet indicate digits greater than 9. For example, for hexadecimal numbers (base 16)a throughf are used.

If the specified number value is negative, the sign is preserved. This is the case even if the radix is 2; the string returned is the positive binary representation of the number value preceded by a- sign,not the two's complement of the number value.

Both0 and-0 have"0" as their string representation.Infinity returns"Infinity" andNaN returns"NaN".

If the number is not a whole number, the decimal point. is used to separate the decimal places.Scientific notation is used if the radix is 10 and the number's magnitude (ignoring sign) is greater than or equal to 10²¹ or less than 10^-6. In this case, the returned string always explicitly specifies the sign of the exponent.

console.log((10 ** 21.5).toString()); // "3.1622776601683794e+21"console.log((10 ** 21.5).toString(8)); // "526665530627250154000000"

The underlying representation for floating point numbers is base-2 scientific notation (seenumber encoding). However, thetoString() method doesn't directly use this most precise representation of the number value. Rather, the algorithm uses the least number of significant figures necessary to distinguish the output from adjacent number values. For example, if the number is large, there will be many equivalent string representations of the same floating point number, andtoString() will choose the one with the most 0s to the right (for any given radix).

console.log((1000000000000000128).toString()); // "1000000000000000100"console.log(1000000000000000100 === 1000000000000000128); // true

On the other hand,Number.prototype.toFixed() andNumber.prototype.toPrecision() allow you to specify the precision and can be more precise thantoString().

ThetoString() method requires itsthis value to be aNumber primitive or wrapper object. It throws aTypeError for otherthis values without attempting to coerce them to number values.

BecauseNumber doesn't have a[Symbol.toPrimitive]() method, JavaScript calls thetoString() method automatically when aNumberobject is used in a context expecting a string, such as in atemplate literal. However, Numberprimitive values do not consult thetoString() method to becoerced to strings — rather, they are directly converted using the same algorithm as the initialtoString() implementation.

Number.prototype.toString = () => "Overridden";console.log(`${1}`); // "1"console.log(`${new Number(1)}`); // "Overridden"

Examples

Using toString()

const count = 10;console.log(count.toString()); // "10"console.log((17).toString()); // "17"console.log((17.2).toString()); // "17.2"const x = 6;console.log(x.toString(2)); // "110"console.log((254).toString(16)); // "fe"console.log((-10).toString(2)); // "-1010"console.log((-0xff).toString(2)); // "-11111111"

Converting radix of number strings

If you have a string representing a number in a non-decimal radix, you can useparseInt() andtoString() to convert it to a different radix.

const hex = "CAFEBABE";const bin = parseInt(hex, 16).toString(2); // "11001010111111101011101010111110"

Beware of loss of precision: if the original number string is too large (larger thanNumber.MAX_SAFE_INTEGER, for example), you should use aBigInt instead. However, theBigInt constructor only has support for strings representing number literals (i.e., strings starting with0b,0o,0x). In case your original radix is not one of binary, octal, decimal, or hexadecimal, you may need to hand-write your radix converter, or use a library.