JavaScript Number toString() Method

What You’ll Learn

Number.prototype.toString() turns a number into a string (same API as MDN Number.toString). Optional radix chooses base 2–36 for binary, octal, hex, and more. This tutorial covers syntax, negatives, scientific notation, five examples, and try-it labs.

Introduction

Numbers are great for math; strings are great for display, URLs, and colors. toString() is the built-in bridge: (255).toString() is "255", and (255).toString(16) is "ff".

Unlike string concatenation alone, the optional radix argument lets you print the same value in many bases without writing your own converter.

This page is part of JavaScript Number Methods. Related formatters include toFixed(), toPrecision(), and toExponential().

Understanding the toString() Method

Call number.toString() or number.toString(radix) on a number primitive or Number object. You get a string; the number itself does not change.

For radices above 10, letters a–z stand for digits 10–35. Hexadecimal (base 16) therefore uses a–f.

📝 Syntax

General form of Number.prototype.toString:

number.toString()
number.toString(radix)

Parameters

• radix (number, optional) — integer from 2 to 36. Default 10.

Return value

Always a string for the number in the chosen base. Special cases:

Exceptions

• RangeError — radix < 2 or > 36.
• TypeError — called on a non-Number this value (for example a plain object).

Common patterns

(10).toString();           // "10"
(6).toString(2);           // "110"
(254).toString(16);        // "fe"
(-10).toString(2);         // "-1010"
parseInt("ff", 16).toString(2);

Examples Gallery

Examples follow MDN patterns. Use View Output or Try It Yourself for each case.

(17).toString();  // "17"

17

(6).toString(2);  // "110"

110

(254).toString(16);  // "fe"

fe

(-10).toString(2);  // "-1010"

-1010

parseInt("FF", 16).toString(2);  // "11111111"

11111111

🚀 Common Use Cases

• UI labels — turn scores and counts into text for the DOM.
• CSS / canvas colors — build #rrggbb with toString(16).
• Debugging bits — print flags with toString(2).
• Base conversion — pair with parseInt(str, radix).
• Logging — readable snapshots without locale grouping.
• Not for money decimals — use toFixed or a decimal library.

📝 Notes

• Does not change the number — returns a new string.
• Radix outside 2–36 throws RangeError.
• Large / tiny decimals in base 10 may use scientific notation.
• Floating-point rounding can surprise you on huge integers — see MDN’s precision note.
• Overrides Object.prototype.toString; Number has its own algorithm.
• For locale grouping (thousands separators), use toLocaleString().

💡 Best Practices