Number.prototype.toString()

Baseline Widely available

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

The toString() method of Number values returns a string representing this number value.

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Syntax

js
toString()
toString(radix)

Parameters

radix Optional

An integer in the range 2 through 36 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 if radix is less than 2 or greater than 36.

TypeError

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

Description

The Number object overrides the toString method of Object; it does not inherit Object.prototype.toString(). For Number values, the toString 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 through f 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.

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

js
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 (see number encoding). However, the toString() 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, and toString() will choose the one with the most 0s to the right (for any given radix).

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

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

The toString() method requires its this value to be a Number primitive or wrapper object. It throws a TypeError for other this values without attempting to coerce them to number values.

Because Number doesn't have a [Symbol.toPrimitive]() method, JavaScript calls the toString() method automatically when a Number object is used in a context expecting a string, such as in a template literal. However, Number primitive values do not consult the toString() method to be coerced to strings — rather, they are directly converted using the same algorithm as the initial toString() implementation.

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

Examples

Using toString()

js
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 use parseInt() and toString() to convert it to a different radix.

js
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 than Number.MAX_SAFE_INTEGER, for example), you should use a BigInt instead. However, the BigInt constructor only has support for strings representing number literals (i.e. strings starting with 0b, 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.

Specifications

Specification
ECMAScript Language Specification
# sec-number.prototype.tostring

Browser compatibility

BCD tables only load in the browser

See also